Thank you, somewhatshocked, I do have a local water report and I don't see anything I think I should be worried about. I test for GH, KH, pH, No3, Po4, and Iron. However, I use RO/DI water for this tank and the TDS meter on the RO unit and the handheld meter read the same. I do a 50% water change weekly. My TDS always reads 300-400+. I use GLA PPS-PRO fertilizer method and I'm wondering if this is the reason for the high TDS readings. So, I would like to add some shrimp and snails to my tank but was worried about the high TDS readings and if invertebrates would tolerate my TDS level.