I measure iron levels before adding CSM+B to make sure I don't go over 0.5ppm. I change some water when I change the filter, 2.5 gallons maybe every two weeks. I did few 90% water changes in the past maybe 3 months apart. I know it is not supposed to be healthy for the fish but nobody died and I have a farlowella inside. Nitrates are at 10ppm in the evening and they go up to 20ppm in the morning. I think it would be best to get that $30 potassium test kit.