2 part dosing and salinity issues

[Syntax1325]

I switched from using kalk in my ato to using BRS 2 part solutions for my CA/Alk/Mag needs last spring. My parameters are pretty stable except I'm noticing that my salinity creeps up between water changes. I have a 125 gallon tank with a 40 gallon sump... I estimate about 115-120 gallons of total water volume. I change 20 gallons of water every two weeks.

I'm currently dosing daily with a Pacific Sun Kore 5th doser 120ml of ALK solution, 120ml of CA and 35ml of Mag... for some reason my tank seems to use a lot of mag.

My salinity raises about number a week, let's say from 35 to 36. It's been two weeks since my last change and my salinity was 37 this morning. My target salinity level is 35. Yes, I use a calibrated refractometer, I'm very meticulous when it comes to keeping my equipment in working order.

Question:

Does this seems normal? I realize that the calcium solution will turn into salt after the corals extract what they need, but this seems like an excessive change. I guess it is what it is. Also wondering if anyone else experiences this amount of salinity change?

[downbeach]

Are you calibrating your refractometer with a 35ppt solution or water? You top off with RO/DI water right? That does look like an excesive amount of Mg, typically its about 10% of your Ca uptake, and kept up with regular WC's. It might be prudent to get a second opinion on the Mg testing.

[laga77]

Yes. 2-part dosing can raise your salinity. Mine goes up like yours. I have an ATO, so I just pull water from my tank and let the ATO refill with fresh water to compensate.

[Syntax1325]

Are you calibrating your refractometer with a 35ppt solution or water? You top off with RO/DI water right? That does look like an excesive amount of Mg, typically its about 10% of your Ca uptake, and kept up with regular WC's. It might be prudent to get a second opinion on the Mg testing.


Yes, I'm using RO/DI. I'm using a red sea refractometer and calibrating as they recommend, with RO/DI and check it against distilled water. I do have 35 solution and it checks out as well.

I have a salifert and a red sea mag test, both are within 40ppm of each other so I'm fairly certain things are correct.

[Syntax1325]

Yes. 2-part dosing can raise your salinity. Mine goes up like yours. I have an ATO, so I just pull water from my tank and let the ATO refill with fresh water to compensate.

Good to know I'm not the only one... it's annoying as [profanity] to have to make corrections.

[Jonny5s]

calcium chloride and the mag are both salts. don't think the soda ash is tho. for me i take water from tank to thaw food and screen food out and dump water down drain dump food in tank. if needed take a bit extra water to thaw food faster lol. also helps stop add extra nutrients to tank

[dkeller_nc]

Something does sound a bit off. A one part per thousand rise in salinity is one gram per liter, and 120 gallons is 465 liters. So your measurements would imply 465 grams of salt equivalent per week.

120 mL daily of a Calcium chloride solution would be 840 mL per week. The alk solution would be the same, for a total of 1680 mL of solution per week. Recipe 1 of the Ca/Alk scheme results in solutions that are about 0.9 moles/liter, so you're adding 1.5 moles per week.

In sodium chloride terms, that's an equivalent of 88 grams. Way below what your observations would indicate. Typically, there's a good bit of uncertainty in specific gravity/refractive index/conductivity measurements, and that would be where I'd guess the discrepancy lies.

[Jonny5s]

would adding salt from the mag dosing change the math much? mag is 2 different salts added together. I also have noticed that the physical size of the pre mix salt patch from brs for 20 oz mix is almost the same amount added for 1 gallon of calcium mix.

[dkeller_nc]

No, I ignored the magnesium mix because it's a whole lot less than the Ca/Alk and doesn't change the answer much.

If you want to check the BRS directions and have a kitchen scale, you can weigh the ingredients and compare it to Randy Holmes Farley's original article that has measurements in grams per gallon for the Calcium and Alkalinity parts.

[Jonny5s]

gallon of alk is 2 cups. 8oz dry cup?
gallon of cal is 2.5 cups
gallon of mag 5 cups one mag salt and 2 cups other mag salt
mag is 3 times the salt in volume.
not sure if it adds up to be much in salinity but this is on brs containers
weights vs amount vs salinity vs whatever sounds like a headache to me.

[disc1]

calcium chloride and the mag are both salts. don't think the soda ash is tho.

The soda ash is indeed a salt.

The issue is that as you dose the calcium chloride and the sodium carbonate into the system, the carbonate and calcium get used but the sodium and chloride stay behind. It is equivalent to adding table salt to the tank every day.

[bertoni]

David is correct. The leftovers of the primary ingredients of the 2-parts are sodium and chloride, so SG always rises in tanks getting them. Often, water changes seem to be enough to keep the level in line, but not always.

[droog]

If you dial in the skimmer to skim wet, you can net out the salinity increase from the 2-part with the salinity export of the skimmer.

-droog

[rvlcf]

I have the exact same problem, dosing the BRS CA/ALK/MAG.