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CaSO4 sources, what am I getting?

Hufsa

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Hi all.
My box of premade GH powder is almost empty and want to start making my own with CaSO4 and MgSO4.

For MgSO4 I am fairly confident as I have some from Aquaplantscare.uk and theres only one variant of this which is MgSO4.7H2O.
I dont know the grade of this (percent purity), so if anyone knows I would like to know as well. As in, is it 95% pure or 99% etc.

For CaSO4 I have some powder from a relative, where it only says CaSO4 technical grade. I assume it was bought from a source for making figures, casts and that kind of stuff.
I know technical grade is not ideal, it will contain more traces of other stuff.
Is technical grade a no go for a fish tank?
My second question is, what is this CaSO4 likely to be, CaSO4.1/2H2O or CaSO4.2H2O?

Ive got half a mind to find a higher purity Calcium source somewhere else. Someone suggested getting it from a brewers shop.
They also only list CaSO4 without mentioning the "crystal water" amount. Im not sure what crystal water is called in english but I hope you understand what I mean.

What kind of CaSO4 would I be getting from a brewers shop? I assume they only sell foodgrade Calcium, and foodgrade should be safe yes?
 

ceg4048

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Hello,
You can use any grade you can find. The tank inhabitants do not really care. MgSO4 is simply Epsom's Salts, which you can find in any pharmacy. I see no need to obsess over "purity". This only forces you to pay more money than necessary.

Also, you should have a look at the water report for your area. Unless you live in a soft water zone your water probably is already high in Calcium and you need only microscopic amounts of Calcium for plants.

Cheers,
 

dw1305

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Hi all,
My second question is, what is this CaSO4 likely to be, CaSO4.1/2H2O or CaSO4.2H2O?
The hemihydrate is what we call "Plaster of Paris", it is a white powder, if you mix it with a small amount of water it will set as a white solid, but will eventually go into solution. The dihydrate is "Gypsum" which will go into solution. It is a translucent crystal. I'd be surprised if yours wasn't the hemihydrate.
"crystal water" amount.
Same "water of crystallization".

cheers Darrel
 

Hufsa

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Thank you both for the replies, really appreciate it 🙂
The calcium stuff I have is definitely a fine white powder and not translucent crystals. And it does like to set into lumps unless shaken out vigorously in water.
Since I know what it is now I will be able to get the correct dosing :thumbup:
I had to go out and buy another tub of commercial remineraliser since I ran out and needed to do a water change, but after this one is used up ill be able to make my own with the loose salts.

I do have quite soft water, the water report says it has 20 ppm Calcium, and when I test it I get 3 dGH from the tap.
I add a Ca and Mg remineraliser to get to 6 dGH as it seems to help my shrimp molt.
 

Hufsa

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The dihydrate is "Gypsum" which will go into solution.
Does this mean that it is more easily soluble and therefore preferable?
The commercial remineraliser I use looks like its using the hemihydrate, what could be the reason for that? Is the hemihydrate less costly perhaps?
 

rebel

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Does this mean that it is more easily soluble and therefore preferable?
The commercial remineraliser I use looks like its using the hemihydrate, what could be the reason for that? Is the hemihydrate less costly perhaps?
I use hemihydrate (designed for gardens) and epsom salts. It works fine.
 

dw1305

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Hi all,
Does this mean that it is more easily soluble and therefore preferable?
Not really, the hemihydrate will become the dihydrate on the way to dissolving. You get quite a big release of heat (the reaction is exothermic) as the bigger crystals form.

Neither form is very soluble (both have solubilities of only about 2.5g in a litre), the slight difference is just the difference between initial levels of hydration. Calcium chloride (CaCl2.6H2O) is a <"lot more soluble">.
Is the hemihydrate less costly perhaps?
I'm not sure, I've seen raw gypsum crystals imported from Spain for the plasterboard industry (by Lafarge at Avonmouth), but never anywhere else. Plaster of Paris is very widely used, and certainly easier to obtain.

cheers Darrel
 
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