Magnesium sulfate is also called Epsom salt, though Epsom salt is a little bit different. If you have Epsom salt you can dose it directly into the water when you are preparing to fill the tank and when you do water changes. It dissolves fast. It usually does not have to be dosed mid week. If you are testing and finding that the plants are removing it faster, then go ahead and dose as needed. Are you also making sure you have enough calcium? The GH test is measuring both, and not distinguishing between these two minerals. You can also test for either Mg or Ca then calculate the other. (It is not just subtracting from the GH test, research the right math formula)
KCl would be a source of both potassium and chlorine, but plants need so little Cl and so much K that I would not use JUST KCl as the source of K. Figure out how much Cl you want, and that will be so little that it will not really count as a potassium source.
KCl would be a source of both potassium and chlorine, but plants need so little Cl and so much K that I would not use JUST KCl as the source of K. Figure out how much Cl you want, and that will be so little that it will not really count as a potassium source.
