Discussion: Alkalinity vs calcium

[Achilles Tang]

Just like to kickstart a discussion on the importance of Alkalinity vs Calcium with regards to coral growth.

Too many reefers I know, even our senior reefers, pay more attention to calcium levels than alkalinity levels.

Why is this so?

I have personally noted that drops in alk levels do have a much larger impact on my corals in terms of noticeable growth and lost of colouration rather than a drop in cal levels.

I personally deem alk levels more important than calcium levels.

What's your take on this?

AT

[FuEl]

Hmmm..I'm no expert in this field..but would just like to give some of my views..alkalinity has direct effect on the buffering ability of seawater. A stable pH would be more crucial to corals rather than an optimal level of calcium. A temporary depletion of calcium will not kill your coral straight away but only slow down its growth. However, a fluctuating pH everyday could really stress any coral.

[Morgan]

Talking about me huh.............It is not that I don't want to raise the Alkalinity but it just that it got depleted really fast.

My Calcium level is also on the low side..

You should see my tank now....the coraline is growing like crazy on the sides of the tank ###### out what I am dosing.

Current level if anyone is interested are

Alk between 5~7

Ca 320ppm

Dosing CA Chloride and Reef Builder everyday.......this is feed thru a constant drip.

I also have a CA reactor running but this cannot keep up with the demand. Coral chips for the reactor is lousy as they don't dissolve as easily as what I expected.

Overall the growth of the sps is very good.

Next plan is to change the reactor media.......

[Mellow]

i think alkalinity has a greater impact on my tank...as said earlier, it has an impact on the ph if the alkalinity is too low...as for calcium, i think as long as it is above 400, i think it doesn't really matter as much whether is is 400 or 450. whereas for dkh, a high dkh of about 12 would certainly help lessen ph fluctuations while maintaining anything at 8 or below is not as good...i've read somewhere where there are people who actually have dkh at 14-15..other views?

[pospeh]

I dont think the main reason that we are concerned about alkalinity is because of its ability to resist ph changes.

Sure, its nice to know that your tank water can resist ph changes when you drip kalk or turn off the lights, but thats not the key.

What we actually want to measure with our standard alkalinity test kits is the content of carbonates and bicarbonates in the saltwater.

Remember, coral skeleton is composed of calcium carbonate. They need both calcium and carbonates (and bicarbonates is converted carbonate) to build their skeleton. They cannot do one without the other.

Because carbonates and bicarbonates are the principal contributors to saltwater alkalinity, we use a test on alkalinity as a surrogate measure of carbonates and bicarbonates in the saltwater.

And that is why the "so-called" reef buffers is composed principally of carbonates and bicarbonates. We are actually addiing them to increase the carbonate and bicarbonate content in the seawater, not to buffer the ph.

So in a sense, the equivalent German nomenclature dKH (degree of carbonate hardness) is actually more descriptive of what we are really after.

[mv3i]

here's something basic

[Achilles Tang]

Got this off somewhere:

In studies, coral growth is supposedly judged to be alkalinity limited and not calcium since there are about 9 or more (milli) equivalents of calcium per litre in NSW vs only about 2.5 of alkalinity. Scientists measure the calcium uptake of reefs by the alkalinity depletion rate.

Coral skeletons are basically a 1 to 1 ratio of Ca to carbonate so worrying about Ca is not really relevent?

Morg, yeah but I used to wonder why you guys could have low alk and not want to top up with sodium bicarb as anxiously as I do. FYI, within 5 days (without topping up), my alk can drop from 12 to 5 without supplementation. A change in colour is also noticeable.

Hence, I really want to get an oversized reactor ASAP to cope with my cal and alk intake coz this manual dosing is taking up my time on a daily basis.

I am overdriving my Koralline reactor so much that my PH can drop to 7.9 at night, what's worse is that my evaporation rate is so slow since my Titanium chiller's doing its job well. Perhaps I should use a fan to speed up my evaporation rate so I can dose kalk more often?

My personal observation is that even though cal levels can still be within the normal NSW range, 360+, growth tips of my SPS corals will visibly show less growth, body colours will darken slightly (well, enough to freak me out) when my alk drops by at least 4 to 5 dKH.

Also they coincide with tissue recession on some colonies? Not too sure if its lack of light on the underside or weaker water currents? hmmm...

[yazid]

I'm still clueless about my water chemistry problem...

But this is my reference Solving Calcium & Alkalinity Problems

Still figuring...

[IanJ]

AT

I put the tissue recession, that i also see, down to the change of lighting that newly introduced wild colony's experience. It seems to make no difference where i put my corals many of these colony's show recession on and in the centre of the base.

If you grow a frag to a colony, in my experience tissue recession appears less of a problem since the frag grows and adapts to the available light. Once the colony grows too large then some base die off is expected, but this can be correlated to what happens on a reef.

Just my thoughts

[Morgan]

In my tank, those colonies that has tissuse recession are those that had been "attacked" by flatworms. I don't see the relationship between low Alk and tissuse recession.

Tissuse recession from bottom of the colonies happen when there is not enough water flow and lights. IMO water high in nutrient is the main cause of tissue recession.

I also realize that the skeleton get very brittle if Alk is low......anyone had this phenomenon

[Mellow]

i dun think we can point out just one factor that causes tissue recession. they are so many other factors that we should also consider, in addition to the basic factors like insufficient lighting at the base and low water movement. coral diseases, water paramters are just as important IMHO. i would prefer to look it as a whole package of factors instead of just ruling out one factor primarily causing it. i suppose everything little thing will have an effect on our prized sps though we may not see an immediate impact....

[Achilles Tang]

Arrgh... getting off topic!

Anyway, what alk levels are you guys aiming for?

For my SPS tank, I am aiming for it to be around 10dkh - 12dkh.

[pospeh]

Here are some key excerpts from an article by Randy Holmes-Farley, which indicates that alkalinity is more important than calcium.

On Calcium.

"Reefkeeping hobby lore has it that boosting the calcium concentration above natural levels of 410 ppm does little to enhance calcification in most corals. That idea is supported by experiments on Stylophora pistillata where calcification becomes limited by calcium at levels below natural levels, but is not increased above about 360 ppm"

On Alkalinity

"Unlike the calcium concentration, it is widely believed that certain organisms calcify faster at higher alkalinity than in normal seawater. This result has also been demonstrated in the literature, where it has been shown that adding bicarbonate to seawater increases the rate of calcification in Porites. In that case, a doubling of the bicarbonate concentration resulted in a doubling of the calcification rate."

So I do aim for 10+dKH in my tank.

Hope this helps.

[Achilles Tang]

Yup... SPS keepers should not worry excessively about calcium levels but more on the upkeep of high alkalinity levels.

[Morgan]

Arrgh... getting off topic!

Anyway, what alk levels are you guys aiming for?

Aming to maintain at local NSW level so when I change water there will not be a drastic shock to the tank.

ALK 6~7 dkh

CA 350ppm

[robe]

I would say alkalinity matters more than calcium but calcium should not be too low either. Either way there shoudl be a balance. if you could have 360 ppm calcium and 8-9 dkh that would be enough.

Don't get too hang-up on this or this might be higher. Just observe your tank. If you sps grows fast but brown or becomes colorful but slow growth, both are successful in my opinion.

Most trials done show that high dkh leads to more colorful corals.

[Mellow]

Arrgh... getting off topic!

Anyway, what alk levels are you guys aiming for?

For my SPS tank, I am aiming for it to be around 10dkh - 12dkh.

i'm still trying to bring up my dkh to about 12...but my dkh seems to be sapped up by the coralline growth. curretnly around 9-10 dkh...by the way, i've heard alot from u guys that calcium gets depleted really fast by coralline growth but mine seems to be the other way round...the dkh goes down really fast as compared to my calcium level... been dripping 6tsp of reef builder for my 3 ft tank every 3 days just to maintain at 9-10dkh...in addition to my daily kalk additions...

hey pospeh, that info was good!!!

[onghm]

by the way, i've heard alot from u guys that calcium gets depleted really fast by coralline growth but mine seems to be the other way round...the dkh goes down really fast as compared to my calcium level

Its normal to perceive that alk drop a lot faster than cal.

For every takeup rate of 20ppm calcium, alk would be 2.8dkh.

That's the balance ratio (20ppm to 2.8dkh)

Assuming :-

1) current reading is 425ppm and 9dkh

2) daily takeup rate is 20ppm/2.8dkh

After 24hrs,

your cal would be 405ppm; dropped by less than 5%

your alk would be 6.2dkh; dropped by more than 30%

So its perceived that the alk is depleting a lot more than the calcium.

But in actual fact, they are just depleting in balance ratio.

Above are just illustration based on my understanding.

Hope I'm right

[danano]

I aim for Ca 400+ppm and Alk 9+dKH

[Joe_P]

I aim for Ca 400+ppm and Alk 9+dKH

I'm aiming for 12 dKh....

notice that my calcium reactor holds that reading easily .... but that was when my reef was partially stocked...... now, I give up......

[Tanzy]

Calcium is actively pumped against a concentration into the coral from the seawater, therefore, a higher concentration of calcium in the seawater will facilitate transport as the concentration gradient is less and since it is mediated by a carrier protein or pump, it can become saturated. According the studies, it seems that the pumps are saturated once Ca reaches 360 ppm. In other words, you have runned out of doors for the Ca to enter the cell through. The next things is how accurate are the testkits. Often, to make up for possible error, reefers tend to bump the Ca level up to a high level of 450ppm to be on the safe side.

Alkalinity is very important. If it is low and bioload high, the pH fluctuation will be stressful to the inhabitants of the tank. Although the mechanisms of calcification are unclear, it is hypothesized that the coral does it by increasing the concentration of both Ca and carbonate locally near the growing skeleton matrix resulting it the precipitation of the insoluble calcium carbonate crystal aragonite. This process is pH sensitive, at higher pH, it's 'easier' to precipitate the crystal. Of course in reality it is much more complicated because there are amino acids and other stuff incorporated as stabilizers. As higher concentration of carbonate or alkalinity tends to allow a higher pH within the cell, it will facilitate calcification by the abovementioned mechanism. Carbonates are not concentrated within the cell in the same way as Ca and I do not know what is the saturation level if it should exist.

Therefore, I feel that we can be arbitrary about Ca level, perhaps 400 ppm will be fine but alkalinity should be as high as reasonably practicable, maybe >10 dkH.

While we are on this topic, I think it would be good to point out that dKH is degree of karbonat(carbonate and bicarbonate only) hardness and not 'Total alkalinity' which includes all buffering ions (carbonate, bicarbonates, acetates, borates, etc). The testkits we use are misleading as they measure total alkalinity but give their units as dKH when it should really be meq/L.

Then it brings on to a related topic of how to acheive high total alkalinity without relying heavily on carbonates and bicarbonates because of their fragile ionic equilibrium. It is quite difficult to achieve and maintain 12 dKH of just carbonate and bicarbonates with a high level of calcium, so borates can help. Think about that.

[IanJ]

http://reefcentral.com/forums/showthread.p...threadid=262217

For a new angle on Alkalinity vs calcium

*Broken link fixed*

Edited November 10, 2003 by Tanzy

[bawater]

As an add on to tanzy's explanantion,

Calcification in the stony corals occurs under the basal disc of each polyp.This biomineralization zone is well removed, on the scale of a millimeter to a centimeter from the photosynthetic region occupied by the zooxanthellae, which is typically located in the upper part of the polyp. (this would be one reason for good water circulation). It seems highly unlikely that carbon dioxide removal and elevated pH is a direct driving force in coral calcification, but it is almost certainly an important factor.

It seems that membrane pumping of calcium ions to, and hydrogen ions from the enclosed spaces between the basal disc of the polyps and aragonite skeleton is the key to control of calcification by the animal.

Carbon dioxide molecules diffuse through membranes and cells to the calcification site.The removal of hydrogen ions greatly raises pH in the calcification area beneath the polyp causing the reaction between water and carbon dioxide to shift to dominance and supersaturation by carbonate ion. With calcium being pumped in, once aragonite crystallization has started, calcification occurs rapidly.

As an equation for every one molecule of CO² taken up and calcium carbonate laid down, two ions of bicarbonate are used and two molecules of CO² are produced.

Since the build up of acidic conditions and excess carbon dioxide would soon slow the calcification process, the removal of CO² by the coral zooxanthellae is critical to continue rapid calcification.

Calcification by the described process supports photosynthesis, providing the preferred low energy carbon CO², which is in very short supply under typical reef conditions of high pH. Photosynthesis in turn supports calcification -locally removing the the acidifying CO². Thus the symbiosis between the animal part of the coral and the zooxanthelle is far more than just an exchange of nutrients and CO² for sugars. (different genera of species utilize these elements in a variety of ways).

Research done (by Goiran ,1996;Al Moghrabi ,1996) on dissolved inorganic carbon utilization by stony corals generally supports the above information.

i also believe amino acids(as any living thing needs)and borates play a part and dose seachem reef plus(recommended by G.A.R.F) which includes in trace form:

boron,bromine,cobalt,copper,iodine,iron,manganese,molybdenum,nickel,rubidium,

tin,vanadium,zinc,arginine,glutamate,lysine,tyrosine,choline,inositol,niacine,

pantothenate,riboflavin,thiamine,vitamin B and vitamin C.

[yazid]

Getting complex...

Anybody did any test on Magnesium? Can this be a factor for Alkalinity and Calcium problem.

Mine reads 1100.

[Tanzy]

Magnesium from 900 to 1600 ppm is OK.