Acropolis

[JiaEn]

Crocea clam on the sand bed spawned yesterday. 

I take it as an evidence of sufficient PAR on the sandbed,  and the clam is doing well. 

There is growth ring as well. So hopefully it will get bigger. 

[JiaEn]

One benefit of having a large open space is to enjoy the feeding of fishes. 

The labyrinth in the main rockwork provide space for the fishes to high.  Since there is ample shelter at hand,  fishes are relaxed and willing to venture out to the open to feed. 

When the fishes dart out to feed,  it's a great opportunity to observe them without obstruction. If any fish were to show signs of hesitation at feeding,  it's an alarm to be investigated further. 

 

P. S.  I cannot be happier about those Fauna Marin pellets. The fishes seems to be able to digest them very well (based on the observation of their faeces). The feed conversion appears to be high too.  Even as I increased feeding, there is no increase in nutrient level in the tank. 

[JiaEn]

Managed to fix up the cabinet doors just before CNY. 

A hooded aquarium prevents light spill and glare into the room,  it also slightly reduce the noise from fans and water flow. 

The downside of a hood is heat. The enclosed space prevents the lights from cooling properly.  For the longetivity of the lightsets, I decided to vent the cabinet doors.  Although this takes away the seamless look, I can be assured that the leds won't degrade before their time.  A trio of dc fans actively push the hot air out. 

 

If I were to start from scratch, I would opt for a chimney style convection vent at the back of the cabinet, that would offer good ventilation without disrupting the facade. 

 

[JiaEn]

A Case for Chromis

Blue-green chromis (chromis veridis) is often viewed as an underwhelming fish.  Its color is not luminous; its size,  modest.  Generally if you think about a background fish in the reef,  chromis is exactly what you have in mind. 

As I observe the fish feeding today, I took a second look on the chromis. I realised they are not that bland after all.  

 

Scales

In an aquarium dominated by tangs,  aquarists can quickly forget that fishes actually have scales.  The chromis have small but distinct scales,  forming a lattice pattern on the flanks. 

 

Display

Chromis displays as often as the more flashy wrasses. The male have trailing streamers on their caudal fins,  and subtly flashes their dorsal ray to signal dominance. This tiny gesture is often unnoticed unless the aquarist watches closely.

 

Color

The blue green chromis does not have mind bending colors of wrasses.  However,  a healthy fish will exhibit bold,  deep colors. As aquarists,  we can color up fishes just like we color up corals: by giving them good environment and nutrition. 

 

Behavior

Further observation of these fishes can uncover a lot of interesting behavior. How they seek refuge in the corals;  how they bricker among themselves, how nip on the colony of stylophora so that the new growth will be open enough for them to hide inside.  All these are not as impressive as the nuptial dance of wrasses,  or the sparring of the tangs,  but they offer the same insight into the reef live. Which is very different from our own. 

 

All these are true if the chromis is healthy, and the environment is not stressful for it. I guess after all, this is a case for healthy fishes. Give the average fishes a chance, keep them healthy, and let them impress you. 

Afterall,  a healthy chromis looks 100x better than a sick peppermint angelfish. 

 

[JiaEn]

Body Language of a Fish

 

As I observe the fishes in the aquarium,  it becomes clear that fish show their disposition through their body language. By looking at how the fish compose itself, we can have a good understanding of it's condition and mood. 

I will attempt to make some notes here. 

 

Eyes

The eye of the fish is a clear indicator of the health of the fish.  Of course,  a cloudy, injured or popped eye indicates problem with the fish,  but there is more to that. For healthy and calm fish, there is a glint in the eyes, the fish is looking, focusing on somewhere.  If a fish has a blank look,  something is very wrong. 

 

Orientation

The body orientation of a fish paints a clear picture of the health of the fish. Water resistant is much higher than air, it's fundamental for fishes to maintain the posture of least resistance in water. Regardless if a fish is hovering,  or zooming around,  it should not wobble around. Awkward flailing of fins and body signifies a fish losing its muscle prowess or coordination. 

When taking into account of the defence mechanisms,  things gets more interesting. Acanthurus have their caudal spikes,  while angelfish and butterfly have their dorsal spines. These are their defenses. When being threatened,  they point these defensive tools towards their aggressors. Tangs will point the tail towards each other,  while a copperband may lower it's head and raise its spine. 

Such defensive can cause some hurt,  but these are not the tools of aggression most of the time. If you examine the bully and victim,  you will find that most of the injury are effected by the mouth. 

 

Fins

Spreading the fins of the fish make it look bigger and more intimidating. It is an effective way for fishes to exert dominance,  as well as a defence mechanism.  Most of the dominant fish will periodically flash their dorsal fin.  I suppose this is an action to remind the tank mate its alpha status. 

When a new fish is introduced to the aquarium,  due to the stress of the new environment,  it will likely fully spread its fins. In my option, this can cause existing residents to mistake this for aggression,  and lead to subsequent confrontation. (This is my theory why new fish almost always gets a beating.  It's like a in those action movies,  where the protagonist barge into a room and draw a gun for self defence,  only to have the guys in the room aiming the gun at him) 

 

There is more! 

A fish can show many colors. Cowering, confident, night, excited, angry.  By looking at the color of the fish, one can know their mood. 

A fish has some regular behavior,  when they are not doing those enough, it may be a cause for concern.  For instance, tangs spend a lot of time grazing and a bit of time to defend it's territory. If a tang does not graze most of the time,  then something is wrong. 

A fish maybe breathing hard.  Is it because of exertion during aggressive display?  Or is it because of other health concerns like parasites? 

 

I want to be comprehensive, but I can't.  There are so much fine details, as well as useful informationc in fish behavior.That's why I feel it's important to watch the fishes,  and speak their language. Then we can be more competent aquarists. 

[JiaEn]

The Lanceolatus Group Wasses

I have two wrasses from the Lanceolatus group.  Lanceolate means spear-head shaped in Latin. So it's not a leap of logic to expect fishes belong to this group have enlongated,  tapered caudal fins. Such as thus gorgeous splendid pintail wrasse from Reef Builders. 

Image from reef builder (https://images.app.goo.gl/FcuNVPifyXA25Kdr6)

However,  despite the conspicuous pintail, this wrasse is not in the lanceolatus group. Surprise surprise,  the defining characteristics of a lanceolatus wrasse is not in their spear like tails,  but in their dorsal and cheek stripes. 

 

Two Lancers,  One Lance 

These are the two wrasses in my tank from the lanceolatus group. 

The top is roseband wrasse (C.  roseafascia),  the bottom one is flame wrasse (C.  jordani). Although flame wrasse does not have the name sake spear tip tail,  it does have very distinct dorsal stripe,  as well as a stripe on it's cheek. 

I have kept this flame wrasse for slightly over a year. It changes from a tiny female to a terminal male now.  It's still capable of more growth in terms of size though. 

The roseband wrasse is with me only for a month. I bought it as a male specimen and fortunately there is minimal aggression between the two. 

The environment is not the most ideal for them though. Because these wrasses hail from the very deep water environments. So the higher temperatures and the bright light in the aquarium is perhaps not the best for them. They are eating well and relaxed. So all is good for now. Both of these can grow to impressive sizes,  and I'm looking forward to that. 

 

 

[JiaEn]

The Problem of Different Growth 

I had to modify my reefscape today.  This is because the difference in the growth rate of corals. 

The digitata,  which is front and center,  grows rapidly. At first,  this bunch offer a bright body of color for the young scape. Now,  it start to encroach on the top level,  and threaten to over take the microclados and millieporas eventually. 

 This will not do. 

I pull the whole rock,  and placed it on the sand bed. The digitata is so brittle, the rock now looks like just had a hair cut.

Oh well,  at least they grow fast. 

I have not finalized the placement of the digitata rock. Probably will shift it soon. 

[flowy]

On 1/16/2021 at 8:46 AM, JiaEn said:

Designing proper flow for a mixed reef has its challenges. On one hand,  acropora species enjoy copious random flow; on the other hand, fleshy LPS may suffer when blasted with water. These animals evolved to make the best use of their environments.  Now that they are in my aquarium,  I need to try and provide the suitable flow for them.  

A few consideration for flow:

1. A mixture of flow style is beneficial. Have a gentle "gyre" flow to circulate the water,  and a localized strong random flow to cater to sps corals. 

2. The output of a random flow pump decreases rapidly as distance gets further.  That's why a large aquarium requires wavemake on both sides. I would like to keep the second viewing side clear of equipment, so something else must be done. 

3. Rocks and corals create obstruction to flow. It's important to consider this effect with the fully grown colony in mind. 

Presenting, the flow schematic of my Acropolis. 

The return nozzle (red) sits at the top left side. Since the return pumps operate at constant flow rate,  the continous operation generates a gyre flow (white). This flow is relatively low speed except at the water surface near the nozzle. Thus fairly condusive for lps in general. 

The forward flow is far above the rocks and corals.  This minimize flow obstruction and ensuring the gyre flow can be set up properly. On the other hand,  the return gyre flow at the bottom is break up by the rock scape. Some will follow the contour of the rocks and form a upswell, while some will flow around the rock pillars and form back Eddie current. 

Supplement this flow is a pair of jebao wave makers (blue). The operates at randome flow mode. Supplying strong and varying flow (green)  to the core of the rock scape. The open rock work structure ensures the flow goes as far as possible.  The strong random flow reaches about half way into the aquarium. 

There is a region with relatively less flow,  on the right side of the aquarium at the mid level.  This is ok as it is a void space without any corals or rock work. 

Overall I think the flow design is satisfactory. Do let me know your thoughts. 

Hi JiaEn, regarding deciding of your flow, how do you decide what is suitable and efficient for your system to maximize flow to the corals yet not blowing at them directly, as i am stuck on deciding how to place my wavemaker  and i am sure that rockscapes also plays apart in that as well as future proofing when corals "grow"

[JiaEn]

@flowy thanks for reading!  I struggled with the flow question for a fair bit especially since I want to limit the equipment and outlets to a single side. 

 

The immediate choice is to try and turn up the wm and direct it at the main rock scape. Like this simple sketch

The red cross is the wave maker, the  black blob is the rock work.  Before flow hits the rock,  the velocity is very high,  potentially too much for the corals directly impacted by it. When the flow hits the rock work,  it's redirect at different directions, velocity is also deacreased. On the other side of the rock,  there may be some eddy flow, weaker and random.  And further downstream,  the flow rapidly decreases.  This implementation produce mostly very high or very low flow zones. The efficiency is low. 

 

I implement my flow design slightly differently. 

The wave makers are not directed at the rockwork. Instead,  the are pointed in/through open spaces around the rock work. Unobstructed,  the main flow caused by the wavemaker does not deteriorate rapidly. My Jebao slw30 push usable flowrate at least to about 2/3 of the tank. 

The good thing about this design is that, the rock work are supported by the entrained flow (green arrow). Due to the Bernoulli's Principle,  the pressure at the high flow region is low. So the unobstructed flow draws in water from surrounding.  This entrianed flow is sufficient for the corals,  even on the opposite side of the rock work. 

 

Only time will tell if the current configuration is adequate when the coral grow even denser and bigger. But I don't see any reason this won't work for the long run. 

[flowy]

[mention=28684]flowy[/mention] thanks for reading!  I struggled with the flow question for a fair bit especially since I want to limit the equipment and outlets to a single side. 
 
The immediate choice is to try and turn up the wm and direct it at the main rock scape. Like this simple sketch

The red cross is the wave maker, the  black blob is the rock work.  Before flow hits the rock,  the velocity is very high,  potentially too much for the corals directly impacted by it. When the flow hits the rock work,  it's redirect at different directions, velocity is also deacreased. On the other side of the rock,  there may be some eddy flow, weaker and random.  And further downstream,  the flow rapidly decreases.  This implementation produce mostly very high or very low flow zones. The efficiency is low. 
 
I implement my flow design slightly differently. 

The wave makers are not directed at the rockwork. Instead,  the are pointed in/through open spaces around the rock work. Unobstructed,  the main flow caused by the wavemaker does not deteriorate rapidly. My Jebao slw30 push usable flowrate at least to about 2/3 of the tank. 
The good thing about this design is that, the rock work are supported by the entrained flow (green arrow). Due to the Bernoulli's Principle,  the pressure at the high flow region is low. So the unobstructed flow draws in water from surrounding.  This entrianed flow is sufficient for the corals,  even on the opposite side of the rock work. 
 
Only time will tell if the current configuration is adequate when the coral grow even denser and bigger. But I don't see any reason this won't work for the long run. 

Wow thanks for ur detailed and prompt replies with explanations, really helped me understand. But one question lies, does turnover rate really matter?, or as long as the corals (Polyp extensions) are happy, all is good?


Sent from Singapore Reef Club mobile app

[JiaEn]

Turnover of the Aquarium

The flow of the aquarium is designed to serve three different equilibriums. From the largest to smallest scale,  they are DT-sump, DT,  and Boundaries layers. I will attempt to explain each of them and their significance in aquarium keeping. 

 

Boundary Layers

On the very tiny structures,  such as coral surface, the viscosity and inertia of water interacts to produce different flow patterns. Interestingly, corals grow various papillae and ridges to engineer the flow around it.

The reason why this microscopic flow is important is,  as corals use up nutrients, give out waste,  consume or release oxygen,  there is a boundary layer. This could due to the flow characteristics, it could also be limited by diffusion.

One can think of the boundary layer as a limit of how fast corals exchange materials with surrounding water. Therefore the water movement needs to be sufficient so that the boundary layer is not overly thick. So rather than saying the flow must be high/random etc,  I would say that the flow for the corals must be perfusive - sufficient to maintain the correct thickness of the boundary layer on every part of all the coral. 

We can only provide a certain flowrate.  How can we meet the need of all the corals then? Surely they have different flow requirement? 

Yes they do.  And no,  we don't need to worry too much, sometimes. 

 

Flow Engineering of Coral

Imagine some one fire a tic tac using an air rifle, and you try to catch it using two fingers. Easy task?  Corals pretty much need to do this on the daily basis to feed. Turns out, they are good at managing this. Not through flash-like reflexes,  but through tried and true engineering.

Corals such as Montipora grow interesting microstructures to modulate the flow at the surface. Many Acropora alters their polyp distance and branch density to keep the flow optimum. Most amazingly, many millipora grows the entire colony in such a way that the top of the colony slows down the flow,  and redirects them into the deeper core of the colony. 

That's why taking a full colony and transplant it in the tank often result in less than stellar results. The growth was an adaptation to a different environment. Most of these colonies will take time to grow and eventually adapt to the new environment, often with vastly different form. 

Taking a frag or a mini-colony, and allows it to grow out,  will allow the coral to grow based on the available flow. In my opinion,  there is less problem down the road. 

[JiaEn]

Turnover of the Aquarium (II) 

After taking care of the tiny details (hopefully) let's look at the bigger picture

Display Tank Turnover

In addition to have sufficient flow to keep the polyps well supplied, thought must be given to ensure the water in the display tank is as homogeneous as possible. 

The flow in the display tank should preventsm the formation of anoxic pockets. It should also reduce the accumulation of detritus. It's difficult to say for sure how much GPH is sufficient. In my opinion,  if detritus don't accumulate,  then the bulk movement of water is sufficient.  I'm of the opinion that the gyre style of flow is the most effective way to achieve good homogeneity in the display tank. 

Display-sump Turnover

This is another tricky topic.  I use to think that by pushing a lot of water through the sump, I am able to supercharge the filtration system. Now I believe I was very wrong. 

The effectiveness of many filtration methods, such as biomedia, protein skimmer,  GFO reactor,  depends mainly on residence time.  When water pass through the system too fast, the residence time is too short. Many of the desires processes cannot be completed fully. 

Therefore,  the turn over of the dt-sump should be set  according to the required residence time of the filtration system. Not too high such that water exits the sump too fast, also not too slow such that the sump become a very different environment compared to the display tank. 

I would look at the skimmer rating,  and adjust the turnover from there. 

[JiaEn]

@flowy hope the previous two posts are relevant to the discussion. Flow is a challenging topic because it's complex and hard to measure. 

Polyps extension can be a good sign,  but it's not a guarantee the flow of the tank is appropriate. 

[flowy]

[mention=28684]flowy[/mention] hope the previous two posts are relevant to the discussion. Flow is a challenging topic because it's complex and hard to measure. 
Polyps extension can be a good sign,  but it's not a guarantee the flow of the tank is appropriate. 

Thank you for your time and the detail explanation provided!, appreciate it!!


Sent from Singapore Reef Club mobile app

[JiaEn]

Part of the reason why I try and write down all these understanding is actually for two selfish reasons. 

1. To keep track of my reefing understanding. What I know about reefing now is a lot different from what I knew one year ago. And I would like to be able to look back a few years down the road,  and see if/how my understanding has improved. 

2. More importantly,  I hope to have reefer challenge my assumptions. There are so many things which we take it for granted, so much so that it can become a blind spot for me. By writing things out and trying to justify my points with logic and evidence,  it is possible for others to question and disagree. 

I'm hoping to understand reefing better  through these discussions. It would be great for my Acropolis to be like the original, a symbol of open discussion and debate. 

[JiaEn]

Coral Fluorescence 

Coral fluorescence is one of the topic which puzzles me greatly. The florescent proteins and zooxanthellae density are all well studied. But what we do in the hobby, or rather, what works in our hobby, is not well explained by the science behind coral fluorescence. I will attempt to compare the science with practice,  then perhaps we can see if there is any missing pieces of the puzzle. 

 

Coral Fluorescence in Hobby

When it comes to reef keeping hobby,  the ways to achieve good fluorescence for corals,  especially SPS corals,  are well established.  We start with water containing very low level of nitrate and phosphates.  Then we attempt to keep the pH high,  and the "big 3" elements stable. Next,  we use intense light and vigorous flow. Finally, we feed the coral,  with planktonic mix,  amino acids,  and dose trace elements to achieve shining color. 

For most of us,  this works well. 

 

Some of these factors are easy to understand. Having stable water parameter close to the reef environment definitely reduce stress for the corals.  Giving suitable food in the form of planktons and amino acids ensure corals have sufficient nutrients. The intense light encourage the formation of florescent proteins to protect the coral. All these are well and good. 

 

The problem is with the trace elements. 

 

On one hand,  dosing trace elements (such as FM colors, Redsea ABCD)  leads to improvements  in coral color for me (and many others); on the other hand, the idea that trace elements is needed by the corals to form florescent proteins is highly debatable.

In the next post I will list down some facts,  maybe one day we can truely know the mechanism of coral fluorescence. 

[JiaEn]

Zooxanthellae

When it comes to coral color, aquarists often focus on two factors: zooxanthellae and florescent proteins. The zooxanthellae (zoox)  which is a symbiotic organism living within the corals (zoo-: animal, xanthe: yellow). Like the name suggest, zoox are yellow in color. They live within the tissue of coral, grow and multiple based on the availble inorganic nutrients. Coral derives nutrients from zoox,  and in turn provide refuge and inorganic nutrients to support their photosynthesis. 

Since zoox is yellow, its concentration will directly contribute to the golden/yellow color of the coral. When the zoox density increases due to high nutrient availability,  the coral tissue will take on the characteristic brown color. Therefore,  the browned coral is not necessarily unhealthy.

Another important role of zoox is to absorbe lights shining on the coral, thus reducing the light-induced stress experienced by corals. Corals evolved to maximize utilization of lights, such that their tissue is largely transparent,  and their skeleton is pristine white. While it allow more lights to be available for the zoox,  it also provide little defence to photo damage. This is the reason why bleached coral often decline rapidly. 

One part of the coral, which contains very little zoox,  is the growth tip of the corals. The tips are generally pale and fragile. Without the zoox to absorb the light 

[MichelReef]

Picked up much from your well-written article. Thank you very much!

[JiaEn]

32 minutes ago, JiaEn said:

One part of the coral, which contains very little zoox,  is the growth tip of the corals. The tips are generally pale and fragile. Without the zoox to absorb the light 

Accidentally clicked post before completing 

...Without the zoox to absorb the light,  the coral produce florescent proteins to absorb powerful solar radiation, and reduce light stress. This is the reason why corals have fancy colored growth tips. 

The same thing happens when coral bleaches, as the coral tissues loses zoox,  they become vulnerable to photo damage. If the coral have sufficient reserves, they produce florescent proteins to mitigate the damage. That's why bleached corals can look surreal for a while, just before they succumb. 

Excessive zoox,  on the other hand, presents another challenge. During photosynthesis, the zoox produces oxygen. At higher concentrations, this can cause oxidative damage to the coral  tissues. To a certain extent, coral copes with this by expelling some zoox.  They can only do so much though. If the zoox population gets too high,  the coral will fail eventually. 

 

[JiaEn]

Florescent Proteins 

 

While zoox supports life functions of coral,  and gives it the much dispised brown color, the florescent proteins (FP)  are the reason why we try so hard to keep corals in our aquarium. 

FP are complex molecules which require a lot of resources to produce. If coral pays hefty price for these proteins,  they don't do it just to please our eyes. In fact, FP are essential for coral to survive. 

 

FP and Zoox

One important reason for the existance of FP is that zoox are very selective when it comes to the type of light it can use. As it turns out, zoox can only make use of light of certain wavelength (can think of it as color). The wavelengths of light useful for photosynthesis is called PAR.  

PAR spectrum  (https://images.app.goo.gl/v49E7u1a1N1ZADo87 Wikipedia )

The light energy unabsorbed by zoox are wasted,  or worse,  can cause photo damage to the coral tissue.  Fortunately,  coral evolved a mechanism to deal with this two challenges: Florescent Proteins. 

 

Spectrum Shifting and Light

In a nut shell, FP absorbs a light of a certain wavelength (this is called excitation), then release the light at a longer wavelength (called emission).  This achieve two goals:

1. When the wavelength of the light is increased, the energy of the photon is lowered. So even if the light is unused by the zoox,  it will not cause too much harm to the coral

2. When the re-emitted light is at the correct wavelength to be used by zoox, the light energy is not wasted, and coral will gain more food in return. 

Therefore,  it is not difficult to infer the factors which drives the coral to produce FP, and achieve amazing colours.

The light must be intense enough such that corals require protection from photo damage.  The spectrum of the light needs to be predominantly of lower wavelength (higher Kelvin rating) so that they allow the FB to shift the wavelength up.  Hence we arrive at standard reef lighting formula : bright,  blue dominant light. 

[Interlude: for modern lightsets, even for day light appearance, the spectrum is still very blue. Our eyes are not sensitive to blue lights. Therefore even with the elevated blue channels, the aquarium can still have the daylight appearance] 

The advent of LEDs brings about a second challenge. Unlike MH or T5, the spectrum of LED light sets are the combination of each diodes. These diodes have very narrow emission spectra.  Therefore,  although a led light might follow a certain spectrum profile,  it is possible for some wavelengths to be very weak,  or even nonexistent.  If the excitation wavelength for a particular FP is absent, then such florescece will not be observed. 

I believe, when it comes to coral fluorescence, the most important factor is the light. Of course, the coral must be healthy. 

 

Building Florescent Proteins

Many reefers have read about the trace elements. Iron for green,  potassium for red,  iodine for blue etc etc.  Like wise, reefing products reinforce this idea and have various "color" additives based on trace elements. 

With all these information, it's fair to assume that these trace elements are in the FPs,  right? 

Turns out this is very far from the truth. 

 

The animation below shows a typical green fluorescent protein (GFP).

(GFP Movie showing entire structure and zoom in to fluorescent chromophore. (Erin,  https://en.m.wikipedia.org/wiki/Green_fluorescent_protein#/media/File%3AGFP_Fluorescent_Protein_Movie.gif) 

The exterior of the protein is a structure called beta-barrel (green). This structure shields the central chromatophore (yellow) from the surrounding environment.  The chromatophore is responsible for the florescence,  while the beta-barrel minimizes effect of interference from surrounding environment.  Where are the trace elements?  Is there an iron atom/ion in the chromatophore?  Turns out there is none. There is no heavy metals of any kind in the FPs.  Even more surprising, is the fact that many of those "trace elements" can have a chemical quenching effect,  dramatically reduce the florescece of the FPs. 

What is needed for FP building,  is amino acids,  not trace elements. 

 

The Paradox

Therefore,  the paradox.  On one hand trace additives are not a part of FP.  On the other hand, adding trace additive improve the color of the corals. 

Why? 

I'm puzzled. Could any one suggest a possible theory? 

 

[JiaEn]

2 hours ago, MichelReef said:

Picked up much from your well-written article. Thank you very much!

Thank you for your encouragement 

[JiaEn]

Fluctuations 

One of the tenet of reefing is that the parameters need to be stable. How much fluctuation is acceptable?  Is it the best for my reef if parameters don't fluctuate at all?  With the advent of modern reef computer and monitors, more and more reefers see their tank parameters in ever finer resolutions. Inevitably, with the ability to measure,  comes the desire to control. 

Do we need to care if the pH fluctuates by 0.5? Or should we be concerned when kh raises by 1dkh? Is there any benefit to keep the temperature within a 0.5℃ window? 

Just like everything in reefing,  there isn't a one-size-fits-all answer. But let me offer some perspectives

 

Homeostasis : Foundation of Life

Living things have the ability to respond to the environment,  and tries to maintain stable internal conditions. 

Take, for example, a typical Singaporean born and raised in the tropics. The envrioment around him is fairly warm and humid. In a warm afternoon of 34℃, he needs to take action to keep his body from overheating: his skin capillaries dilates, allowing more bloods to carry the heat to the surface.  He also starts to sweat,  cooling down his body through evaporation.  When he travels to Norway on holiday,  where the air is freezing cold,  he has to take actions to keep himself warm.  Blood circulation is reduced to the skin and limbs,  reducing heat loss.  He even shivers every now and then,  generating more heat as the muscle spasms. 

There are a few lessons here for us:

1. Living things can adapt to a changing external conditions

2. There is a window of adaptable condition,  out of which,  survival is unlikely. 

3. The more adverse the environment,  the more energy is spent to maintain homeostasis. 

 

What about Fishes and Corals? 

We need to understand,  the internal environment of a fish or coral is very different from the water in which they reside.  Just like your internal organs have very different properties to the air around you.  

The reef water have very low phosphates,  but corals will use different methods to concentrate phosphates in it's tissue. Reef building corals manipulates pH at some locations, and facilitates the building of calcium carbonate skeleton. There are many complex actions done by the corals and fish.  All these costs energy. 

 

Energy Cost of Adaptation 

Therefore it's not hard to imagine,  if a coral with less energy reserve will have a more difficult time to cope with adverse environment conditions. It's also not hard to accept,  that a coral or fish living in harsh environment, or struggle to adjust itself to cope with fluctuations, may use up more energy than it gains. This energy deficit is really what causes the corals to eventually perish. As the energy reserve dwindles, the organism have less resources to maintain homeostasis,  and eventually,  dies. Thats why often,  corals don't die immediately following a mishap, instead,  they waste away a few days or weeks down the road. That's why, when some unfortunate accident happens,  some corals survive,  and some does not. 

 

So what is the acceptable fluctuation?  One that is well within the limit of adaptation of your livestocks. 

[JiaEn]

To (not) Imitate the Sun

Let's start by putting away the delusion that aquarium lighting is meant to imitate the sun. 

Sunlight striking the surface of the sea is intense,  continous and almost unidirectional. 

Firstly,  the intensity of the solar radiation is very high.  The average solar irradiation on earth surface is 1380 W/m^2. This means for a 3ft tank,  it needs to recieve 566 W of irradiation.  If we assume the LED lights are the most efficient ones, (50% efficiency), we need 1332 W worth of light set to power the 3ft tank.  Crazy,  right? 

Secondly, the solae irradiation is a continuous spectrum, without missing or diminished wavelengths. In the era of LED lights,  we are faced with the possibility of missing spectrum. Although the overall color of the light may look similar,  if the spectrum to excite some florescent proteins are weak,  or missing,  the expression of those colors will be weak or completely absent. 

Lastly. The solar radiation strikes the surface of the Earth more or less parallelly. This impacts the light profile in a really big way. Because the light is largely parallel, it almost doesn't spread further as we get further from the surface. In contrast,  the aquarium lights are generally close to the surface. As the result,  the radiation rapidly spreads out and it's intensity rapidly declines.  This is the reason why,  while some corals thrives over a depth range of more than 20 meters in the wild,  they cannot adapt to the 2 ft of aquarium depth. 

Therefore,  although it's a noble goal to bring sun to our artificial reef,  it's impractical, and ill-advised. 

 

 

[JiaEn]

An image interlude before more walls of text.  

[JiaEn]

The Eyes Deceive 

Continue with the discourse on aquarium lights. There are many nuanced issues which we should take note. Among all the challenges for us to "see" the difference in the aquarium light, the biggest obstacle is our own eyes. 

A quick recap of PAR, the largest peak of the spectrum is in the sub 500nm region. Unfortunately, our eyes are not zooxanthellae. Instead of adapted to the underwater environment, where the most avaible spectrum is blue,  we are terrestrial and is more able to see longer wavelength lights. Therefore even when an aquarium have extremely potent blue spectrum, it can still appear not so "bright". Same happens during solar eclipses,  although the sun looks dim,  the low wavelength spectrums are actually very intense. 

What I'm trying to say is,  it's unreliable to judge the PAR value of the lights based on visual inspection. 

 

The Brain Decieves 

The lights recieved by the eyes activate the neurons and transmit the signal to the brain. The brain processes the signals and piece together the image.  The human visual system is very impressive. Not only does it have an impressive 24 stops of dynamic range (a top tier DSLR have about 16), and it can carry out impressive white balancing on the fly. 

This is why when we look at our aquarium,  we can see both the acropora at the brightest crest,  as well as the peppermint shrimp hiding in the darkest corner. This is also why,  corals looks pleasing enough without the use of a yellow filter. Our brain does the filtering for us. 

Thus the difference between what we see and the heavily filtered photos, is just a matter of preference. Camera or eyes,  there is always filtering involved. For me though,  since I enjoy my aquarium with my eyes,  I prefer to judge the color of coral based on what I see. 

 

The Profile? 

When we turn the blue channels to 100% and white channel to 25%, it doesn't automatically mean that the blue spectrum is 4 times more than the rest.  Depending on the light set,  the number of the LEDs in a channel can be different. For instance,  Radion XR15 G5 has only 12 cool white LED to go along with 24 blue and royal blue lights. It's easy to see that even when all the channels are set to 100%, the overall spectrum is still going to be very blue. 

It's interesting to note that these lights are capable to produce neutral daylight looking aquarium.  It's also important to note, that percentage profile for channels between different brand or model is not a useful comparison.