Tom, I finally managed to get hold of CaCl2, but not CaSO4.

On the pack, it is labeled CALCIUM CHLORIDE anhydrous CaCl2. There is also a warning that say the chemical is corrosive. Molecular weight is 110.99 .

The chemical appear dry. Not 100% powder but most are in the form of lumps. I had to softly hammer it to get it into powder form. Then I scooped 1 tsp and added that into a beaker with some water in it.

I was very surprised that the mixture became very warm !

Is this normal for CaCl2 ? Since it is corrosive, can I safely store in the plastic container and leave it in my tank's cabinet at 32 degree Celsius ?

Please advise. I am very worried indeed

I made a 50% WC then filled up my 160g tank. I waited for about 2 hours, then did another 50% WC. At each WC, added anti-chlorine. Neons and SAEs looks good.

I decided to dose CaCl2 at 4 teaspoons. That will give me 10.63 ppm Ca (with Fertilator). I also added 1tsp MgSO4.

After about 4 to 5 hours I noticed strange behavior with my Congo Tetras. They hide at the back of the tank. Neons seems ok for the moment. But I have 2 dead SAEs. And my Chinese Algae Eater darted across the tank for no reason.

During both WCs, I top up the tank slowly and added anti-chlorine as directed. I just do not know what caused this. I would like to blame the CaCl2 but should I ?

If I recall my chemistry correctly, CaCL2 is exothermic. So it would probably be best to mix it, let it cool, then use for an aquarium.

A quick search on Google for "CaCL2 exothermic" seems to substantiate my recollection here, but perhaps someone who is a chemist can chime in here?

It's the dissolution of CaCl2 that's exothermic, and yes, that's normal. The dissolution of anything in anything is exothermic, IIRC, it's just a question of how much so. If you add water to concentrated HCl the mixture can actually boil (and splash you and burn you.)

Thank you rusticitas and swylie.

BTW, is industrial grade chemicals safe enough for our tank. Or do we have to buy the more expensive lab grade chemicals?

We are just fertilizing, so either industrial or agricultural grade chemicals are fine. If we were doing analytical chemistry it would be a different story.

Thank you for the clarification.