Potasium chloride, is used as the source of potasium to a reef aquarium then the following can be used to make a DIY stock solution.

It can also be added as a dry solid, but it has to be pre-mixed before addition to the aquarium and can be harder to measure out.  

The use of a stock solution gets around both of these problems.

The variables used to make the calculations are as follows:

M0 = Mass of potasium chloride required to make the stock solution (grams)

V0 = Volume of stock solution (litre)

C0 = Potasium concentration of the stock solution (ppm)

V1 = Volume of stock solution dose to give potasium concentration rise of C1 (cm3)

V2 = System volume (litre)

C1 = Potasium concentration rise required in the system (ppm)

Ca = Fraction of the type of Potasium chloride that is Potassium by weight : 0,52441

The value of K depends on the type of Potasium chloride that is used to make up the stock solution. In most cases this will be KCl, so the valve for K in this case is 0,52441.
The concentration of the stock solution, C0, is really arbritary, but the higher the concentration the less of the stock solution has to be added to give a certain system concentration increase. 

Although the higher the concentration the easier it would be to overdose and cause problems.

A good number to start with is around C0 = 100,000ppm, which is the concentration of some commercially available Potasium chloride additives. 
The mass (M0) of Potasium chloride required to add to the stock solution of volume V0, to give concentration C0 is given by:
M0 = ( C0 * V0 ) / ( Ca * 1000 )
Therefore to get C0 = 100,000ppm stock solution, using KCl, M0 = 190,69049 grams is required to be added to V0 = 1 litre.

The equation to determine the volume (V1, cm3) of the stock solution (concentration C0 ppm) required to increase the system (volume V2, litre) potasium concentration by C2 ppm is as follows:

Cmix = ( V0 * C0 ) + ( V1* C1 ) / ( V0 + V1 )
Therefore to increase the system of V2 = 500 litre, potasium concentration by C2 = 430ppm, Cmix = 450 ppm, using a stock solution of concentration C0 = 100,000ppm need to added V1 = 100 cc.

Potasium chloride has a very high solubility, with it being possible to pack up to over 1,000,000ppm into water, which is a highly potent solution.

Take great care when making up these solutions and adding it to a reef aquarium. It would be very easy to over dose if great care is not taken.

Always err on the side of caution, all that will have to be done is to add a little bit more at a later time.

This is much better than putting in too much, it cannot be taken out again without having to do a major water change and sustaining some damage to the inhabitants.
potasium chloride

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