Maintaining Salinity

[Validator]

Hi All,

I started out with a salinity level of 1.027 exactly a month ago and today my salinity level has fallen to 1.022.  I have made some water changes to the tank so far with water I over bought from the LFS.  I am wondering how I am losing salinity.  I read online that there could be a leak which I find highly unlikely since there is no leaks detected.  The other possible reason is salt creep and the protien skimmer.  My protein skimmer only started stabilizing about a week ago and most times I have dumped the over skimming back into the tank.  I have only cleared the skimmer cup once by throwing the water away since the skimmer activated.  So could it be salt creep?

Yesterday I did a small water change and the salinity went up to 1.023 and this morning fell back to 1.022.  What should I do?

[JiaEn]

How do you measure the salinity 

[Validator]

I got a digital refracts meter from the lfs 

[Validator]

This type 

https://www.freshnmarine.com/products/salinity-temperature-digital-tester?_pos=9&_sid=86f07ff9d&_ss=r

[R0B]

You shouldn't see any saline reduction to the level you mention in such a short period of time. There are very few factors that could cause salinity to drop. Usual suspects being...

1. Your salinity testing apparatus is not working or calibrated correctly. This could be caused by simple calibration issues or missteps, auto temp adjustment issues or malfunction, not throughly cleaned, calibration fluid being tainted/not accurate etc). Try testing your RODI water and see if it shows a negative number (if machine can read this)

2 Fresh water / lower salinity water was added into the system. What is/was the salinity of the water you added? Did you test it?

Beyond that there really isn't much to account for a salinity fall.

Before you try and correct it you need to make sure of the issues is an issue suggest you take some water to LFS and ask them to test for you.

Good luck. Let us know how you progress...

[Otaku Reefer]

I got a digital refracts meter from the lfs 

Not expert here, but seems digital salinity meter is using conductivity to measure, and refractometer is using light bending to see the refractive index and hence correlation to the salinity. therefore will have some delta between the measurement methods i think. I am using digital salinity pen to measure 1.025 but LFS water is always 1.021 -1.022 using my digital pen. I tot is my pen not calibrated properly but i use a swing arm to double check and it matches my pen so i didn’t think too much further and lifestock doesn’t seem to care. So i just stick to my pen reading and ensure stability instead of chasing numbers. Hope this helps.


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[JiaEn]

19 hours ago, Validator said:

This type

Pen style conductivity probes can be inaccurate and inconsistent. I would say get a good optical refractometer is a good choice. 

[Validator]

Hi All, Thanks for replying.  Yeah I got the pen type because I was lazy, can just poke into the water and test.  I also have the optical refractometer.  So I took the advice of all and I tried this.

While mixing a fresh batch of salt water for some new live stock.  I tested the TDS and Salinity of my distilled water(Spritzer) and yielded TDS(1 ppm), Salinity(Digital - 1.000) and Salinity(Optical - 1.000)

My tank water yields Salinity(Digital - 1.023) today and Salinity(Optical - 1.026). Is this counted as a big difference? 

[Otaku Reefer]

Hi All, Thanks for replying.  Yeah I got the pen type because I was lazy, can just poke into the water and test.  I also have the optical refractometer.  So I took the advice of all and I tried this.
While mixing a fresh batch of salt water for some new live stock.  I tested the TDS and Salinity of my distilled water(Spritzer) and yielded TDS(1 ppm), Salinity(Digital - 1.000) and Salinity(Optical - 1.000)
My tank water yields Salinity(Digital - 1.023) today and Salinity(Optical - 1.026). Is this counted as a big difference? 

i just found a reply from hanna regarding the differences between conductivity probe vs refractometer. So based on understanding, it concurs to what you and me
experienced. The refractometer might give inflated values compared to conductivity probe due to organics that contribute to the additional light bending but would not contribute to additional salinity. I also read that one cannot use the standard calibration meant to calibrate refractometer for salinity probe/pen calibration. My recommendation is just to stick to one, if u prefer refractometer just stick to it. For me, i more lazy prefer to use the pen haha. Maybe other experts can chime in.

From Hanna instruments reply
What is better for salinity?

When comparing conductivity to refractometery to measure salinity, the consensus among the scientific community favors conductivity. This is because there are non-conductive material which can impact the refractive index of seawater but not the actual salt concentration. For example, if we add sugar to artificial seawater, we will see that our salinity value will increase but we have not changed the concentration of salt in the water. If we measured the salinity of that sample with our HI98319 conductivity meter you’ll notice the value is largely unchanged. It is common to have inflated values with a refractometer due to the large number of materials which will affect the density of that water outside of the dissolved salt values. For example, organic waste, sugars, potential non-ionic contaminants or uneaten fish food can increase the values produced on a refractometer but this would be less likely to occur on a conductivity meter like the HI98319.



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[JiaEn]

1 hour ago, Otaku Reefer said:

The refractometer might give inflated values compared to conductivity probe due to organics that contribute to the additional light bending but would not contribute to additional salinity.

This is possible,  especially with a regular refractometer designed for brine solution and sugar solutions. However  for a properly made and calibrated refractometer for seawater application, it is spot on if you use it properly. 

1 hour ago, Otaku Reefer said:

organic waste, sugars, potential non-ionic contaminants or uneaten fish food can increase the values produced on a refractometer

Yes,  but also,  these will only be present in our reef water at very low concentrations. So it's not that much of a problem. 

 

1 hour ago, Otaku Reefer said:

conductivity meter

This is actually fairly tricky,  because microbubbles or another other inclusion in the liquid between probe junctions are going to mess up the conductivity reading. Also,  the probe need to have temperature compensation and be properly calibrated to achieve a good reading.  So pros and cons I guess. 

 

Anyway I'm splitting hairs here. Either instrument is good,  and we just need to keep the reading from drifting. So even if the absolute value is not correct,  we can still monitor the consistency. 

[Validator]

Thanks all.  I will just need to monitor.  What is the best salinity to keep for reef tanks in general and how may I reach it if it is too low?

[R0B]

The ocean has a salinity of 1.026 so that is a good target although some reefer prefer run a little lower (1.024 to 1.025). Very few people run it higher. So 1.027 is max.

Assumung you want to increase it slowly over time. One way to slowly increase is to add a tiny bit of salt to your ATO. A little more aggressive is to do it over a series of water changes.

[Validator]

Thanks rob I did my first salt water mix so more confident to do it now.