Dolomite Lime is what I use, but I mix it in the soil prior to my grow. I usually mix 2 table spoons per gallon of promix soiless mixture. I don't think you can use it now or if so it won't be that effective. Using it by mixing with water I don't think is what you want. I use it to use as a PH buffer, and ever since using it I have not had any problems with PH.

To correct your problem I would start using a good PH balanced nutrients that contains micro nuttrients. You are probably low on micro's and that is what is causeing your spotting.

Hope this helps and good luck!

TGT