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Remineralisation solution precipitate

Heelllooo

Heelllooo

Member
Joined
6 Jul 2023
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84
Location
Belgium
Hello,

Until now I was mixing tap and DI water for my water change but due to a few reason, mainly simplicity, I want to go the remineralised 0kH DI water route.

So I already had MgSO4.7H2O on hand and I bought this product which is CaCl2.2H2O :

With the plan of mixing 13g of each in 500mL of DI water to make a stock solution for remineralising my DI water.

Issue being the solution precipitate. I've try dissolving each compound separately, which work. But when I mix them, the precipitate appear after a few minute.

Is it normal ?
Could it be because of some impurity in my chemicals ?
Could I avoid this issue ?
 
Heelllooo said:
But when I mix them, the precipitate appear after a few minute.

Is it normal ?
Could it be because of some impurity in my chemicals ?
Could I avoid this issue ?
Click to expand...
Yes it's normal, mixing calcium chloride with magnesium sulfate at close proximity will yield calcium sulfate, from memory, which has a reduced solubility (step forth scientific explanation)

You can solve the problem by dosing the salts separately, but you can't make these chemicals into a stock solution.

I'd love to link you to a simple explanation regards common fertilizer salts reacting with one another, but sadly can't, it was once mentioned... but hey o.
 
Heelllooo said:
Hello,

Until now I was mixing tap and DI water for my water change but due to a few reason, mainly simplicity, I want to go the remineralised 0kH DI water route.

So I already had MgSO4.7H2O on hand and I bought this product which is CaCl2.2H2O :

With the plan of mixing 13g of each in 500mL of DI water to make a stock solution for remineralising my DI water.

Issue being the solution precipitate. I've try dissolving each compound separately, which work. But when I mix them, the precipitate appear after a few minute.

Is it normal ?
Could it be because of some impurity in my chemicals ?
Could I avoid this issue ?
Click to expand...
when you Mix MgSo4 and Cacl together, this form CaSO4 in the solution and since the solubility of CaSO4 is extremely low, what you are seeing is an insoluble CaSo4. your best bet is to use MgCl and CaCl if you want to go with the Solution Route, they both are highly soluble.
 
Hi all,
Happi said:
you still cannot make Proper CaSO4 Solution
Click to expand...
You really have to dry dose it as @Happi says. The problem is that it has very low solubility in water <"Calcium sulfate - Wikipedia">. This applies to all the different hydration states (<"water of crystallization">).

The only way you could make a solution would be to make a saturated solution (with some undissolved CaSO4.2H2O present in the container).

You would need (more than) 2.6g of CaSO4.2H20 (2.6g is the theoretical solubility limit, if you don't have <"any other ions in solution">), made up to a litre with DI water.

I'm going to say 5g of CaSO4.2H2O, but you would need to give it a really good stir when you added it and add it to cold DI water. Of that 5g only ~1/2 will go into solution and 1/2 will be undissolved as solid CaSO4.2H2O.

The RMM of CaSO4.2H2O is 171, the RAM of calcium (Ca) is 40.1 and the percentage calcium (Ca)= 40 / 171 = 23.4%

At 25oC that would supply:
  • In your 2.6g (2600 mg) = you have 608 mg / L (ppm) Ca (2600 x 0.234),
  • so in a 100* litre tank adding the whole litre would supply 6.1 ppm Ca and
  • adding 100 mL (cm3) = 0.6 ppm Ca added.
Which is why you need to use dry dosing.

* 100 litre volume just makes the maths easier. If you don't want any mental maths you could use an <"aquarium dosing calculator">.

cheers Darrel
 
Last edited:
Hi all,
Heelllooo said:
I'm gonna prepare two separate solution, one of CaCl2 and one of MgSO4 and I will dose each of them in my WC water.
Click to expand...
That should be fine, they are both soluble salts.

I'd dose them a little time apart, because of potential solubility issues, even in the tank.

large_solubility_rules_chart-mk-png-png-png-png.png


cheers Darrel
 
To those that use CaCl2 and MgSO4 to remineralise their RO water.

What's your exact process ?

Is everybody dry dosing ?
 
dw1305 said:
I'd dose them a little time apart, because of potential solubility issues, even in the tank.
Click to expand...
I dose solutions of these two one after another without issues. For many years.
 
Heelllooo said:
To those that use CaCl2 and MgSO4 to remineralise their RO water.

What's your exact process ?
Click to expand...
Not ro water but... my process is ~ fill a 10l bucket with tap water and add cacl2, then pour it in the tank. I then fill another bucket with water and add mgso4 and then pour it in the tank. Alternatively add x amounts of cacl2 to you ro water and then add x amounts of mgso4.
It's a simple process and causes no precipitation, this only happens when these salts are mixed in CLOSE proximity, even if there was a reaction cacl2 ~ mgso4 ~ caso4 the solubility level of caso4 in the tank would unlikely get breached and form precipitate.
 
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