Toxins in my discus tank were kept at a minimal for a while. Recently, nitrates jumped up, most likely from over-feeding. A few have some white fungus looking junk on them but most have just turned dark in color. I've added meds today, pimafix, melafix and salt. A 40% water change was done Sat. and another 40% last night. Water temp is 86 and filtration is sufficiant. Nitrates are still high, is it too soon to do another water change? Should I let the meds sit for a while before I do? If I can do another water change tonight, how large of one should I do? Are there any other meds you would recommend I try? Any other tips?