Good morning. After almost two years of undetectable PO4 on Salifert, I purchased a Hanna ULR and have been testing very high at over .2. Salifert still shows 0. I am running my fug at 19 hours a day and skimming heavy. I feed light once a day. I started adding GFO in the sump. Over the last week, the PO4 dropped down to .13 so yesterday I replaced the GFO and today, I’m back up to .19. What is going on? Everything else is in check. NO3 is 7-8. Thanks.
Shawn
Shawn