So I use the Hannah checker for Alk. Refractometer has been calibrated. I will check again. Sand gets vacuumed each week during water changes. I have never had a sump. Simple 55 gallon with hob filter and hob reef octopus skimmer. For the first several years barely detectable nitrates. I use phosguard for phosphate when needed. I know the perception of phosguard but never had an issue with it. I hate the mess of GFO. Weekly 10% water changes. Was using Kent salt but now use fritz salt. Hard to find Kent these days. It still confused me how the GSP, mushrooms, inverts, fish, and anemones are unaffected by whatever it is. Going to order an ICP test.