# How to use plaster of paris as my calcium source???



## bergste (Jul 5, 2013)

I've read a lot about people using plaster of paris as their calcium source. I went and got a big jug of it and tried using it only to find out that it isn't water soluble! Yet, despite this fact, people still manage to make it work. Do I need to let it harden and use it as a root tab?


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## Zapins (Jul 28, 2004)

Not sure why you'd want to use that for the calcium. Plaster of Paris (POP) is basically CaSO4 which is very insoluble in water, meaning it will take ages to dissolve and during that time your water will be milky white. Which can be quite annoying. CaCl2 dissolves easier and is readily available online (ebay and http://www.aquariumfertilizer.com/index.asp?Option1=cats&Edit=2&EditU=1&Regit=2) and I think even in pharmacies and home brewery stores, probably also hydroponics shops.

You can use the fertilator on our website (top left) and choose CaSO4 from the list however, the CaSO4 from POP is not hydrated so when you calculate out how much you need using the fertilator you will need to add less than whatever the fetilator says you should add because POP is missing the water which the fertilator assumes is in there.

I think (though someone should probably check my maths) that you'll want to add about 6% less POP than whatever the fertilator tells you to add for the recommended (CaSO4)2 H2O dose.


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## bergste (Jul 5, 2013)

I appreciate the response thank you. Yeah I agree PoP takes forever and a day to dissolve and it's really irritating. I'll take a look into calcium chloride and see how that goes. Thanks again!


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## Seattle_Aquarist (Mar 7, 2008)

Hi bergste,

+1 for Zapins comment on CaCl; but keep in mind that it creates an exothermic reaction with water (gets hot) so I always dissolve it before adding it to my tank to avoid a fish swallowing a hot pellet of the stuff.

CaCl is easy to find a hardware stores or online. Dri-Z-Air is used as a dehumidifier agent. It is 91% calcium chloride with about 5% potassium chloride and a little trace (1%) sodium chloride. I pick it up at a good local hardware store (not big box); $1.50 gets me a 13 oz bag.


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