Calcium Sulfate to dose Ca on vacation

[behlke]

Could I use Calcium sulfate (plaster of paris) to slowly dose Ca into the aquarium as it dissolves? The idea is to mix plaster of paris with water and then pour it into an icecube tray. Then, when I am gone I can place a couple of cubes in the tank to replenish the Ca as the corals use it to up.

I don't think this will work as a long term solution because the SO4 will increase in the tank, and is probably not a good thing. But for a vacation, I think the plaster would dissolve until the Ca reaches saturation, and then keep the aquarium saturated with Ca until all of the plaster dissolves.

Your thoughts?

[disc1]

Calcium sulfate is pretty insoluble. I've seen a bit of plaster of Paris before but I never saw it dissolve. It just sort of makes a slurry and then hardens again.

[blanden.adam]

The calcium in our aquariums is also not even remotely close to saturated when you look at a freely soluble calcium salt like calcium chloride, but is already super-saturated when considered in the context of calcium carbonate. Not a good idea.

[disc1]

Even if you were talking about using calcium chloride, there still might be issues trying to freeze it. There's a really good reason why that stuff is used to de-ice driveways.

[blanden.adam]

As a point of clarification, I was saying that the idea that you'd hold calcium "at saturation" using any supplement simply wont work. I was not advocating the use of frozen calcium chloride cubes :)

[Twistofer]

The question really is...How long are you going to be gone, and would it really make that much of a difference? How much does your Ca decrease over that period of time? I take it you are dosing once or twice a week, rather than using continuous dosing, like with a Ca reactor.

[bertoni]

I don't think you'd get any sort of controlled dissolving effect, if you got any dissolution at all. Sometimes, there will be some calcium sulfate precipitate in magnesium supplements, and it's probably an ingredient in some 2-parts, but I agree that it's unlikely to be easy to dissolve in saltwater at any significant rate in this application.

[behlke]

Thanks for the responses.

This idea popped into my head when I was working with some plaster. I don't have a deep enough chemistry background to know if it would work or not, so I threw the idea up on RC to get some feedback. It sounds like it will not work because, as I read it, the CaSO4 is already saturated in the water and will not dissolve as needed, like I had hoped.