For my hardness kit you add drop of the solutions to a test tube until the colour changes, each drop is a unit of hardness, but I guess yours could be different. You may want to think a tank upgrade, 12 inches wide isn't much for a tank of adult Discus, a few more inches would make a lot of difference. You really should have waited for your test kits before buying them, how did you know your water was suitable? Hope that doesn't sound really mean, don't want it to be.