I have had Marines on and off since the 70s but I know things have changed a lot since then.I've never found the need To test because all my livestocks are healthy and well In four years I've been running this tank I've never had any hair algae Or any other algae Problems or problems with dissolvable solids but if I was to guess I would say it must be around 300 mark but using the products and My filtration Combined must bring it right down otherwise how do you explain my tank you seen for yourself and my tanks been running 4 years as I say and it has a Number of lps,sps, Soft, Plus a sebae anemone And two bubble tip if there was something bad in the water these will soon let me know as you know I don't condone RO Water it's good stuff but I personally just don't need it and I just wanted to show People out there that it can be done successfully I hope you can understand where I'm coming from