What is potash that you use in the pool?

Potassium chloride appears to be a prescription medication not a pool related product. Stick to the tried and true methods of proper pool maintenance. Liquid 12.5% in strength, dry granular at 99% strength ( anything less than that is cheap and full of inert ingredients), tabs - large or small. You will not be saving money by using the cheap products since it takes more of the lesser grade product to do what the best product will do in half the amount. Potassium is also used in lethal injections in prisons. I also do not know that you could get any quantities to be sufficient to maintain a pool if you could even do that. The cost would be astronomical per pound. For example: google Potassium Chloride in Wikipedia.