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Old 12/08/2017, 11:49 AM   #1
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Anybody use CaSO4 as an additive?

I only ask as I have some lying around for my freshwater plants.
It seems almost all of the additives I have seen on the market are Calcium Chloride...

I am not a chemist, would not know if the Ca would unbind with Sulfate and pair instead with Carbonate...

Seeing if anybody has experimented with this, or terrible idea.

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Old 12/08/2017, 12:57 PM   #2
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Yes, people that supplement Ca will usually use CaCl, unless using kalk (to raise both alk and Ca).

The CaSO4 would disassociate into Ca and SO4, just as CaCl would become Ca+ and Cl-ions.

Two part additives like CaCl will add Chloride over time, which isn't a big deal since there is a lot of Chloride in natural seawater. There isn't as much Sulfate, so using CaSO4 over time could be a problem.

I would get some CaCl. It's pretty cheap.


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Old 12/08/2017, 01:19 PM   #3
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Like nereefpat said, CaCl2 is a better option. There is ~19000 ppm of Cl ion in natural sea water. So if you wanted to increase Ca by say, 50ppm, dosing required amount of CaCl2 will raise Cl by 100 ppm. An increase of Cl from ~19000 to 19100 ppm is not a big deal.

A 50 ppm raise in Sulfate from dosing corresponding CaSO4 can be a problem. Sulfate have the capacity to fuel growth of sulfer reducing bacteria which produce toxic hydrogen sulfide.

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Old 12/08/2017, 03:35 PM   #4
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I agree that calcium chloride is a better choice. The sulfate would be fine if only a small amount is used. There is a fair amount of sulfate in seawater, too:

Jonathan Bertoni
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Old 12/08/2017, 04:30 PM   #5
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Calcium sulfate is not very soluble, about 200 mg will dissolve in 100 ml of water. Of that 200 mg about 1/3 is calcium or about 60 mg. If you wanted to increase the calcium level in 1 liter of salt water using a saturated freshwater solution of calcium sulfate, it would cause a large salinity change.

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