FWIW I run my PO4 between 0.07 and 0.10 and I don't have any GHA. I also run a fuge though. I keep it slightly elevated as I don't have the ULR hanna yet and I don't want it bottoming out, dino's suck. My dumbarse bought the LR one by mistake.... so with with a +/- of 0.04 I keep at a min 0.07 so given the potential error rate I'm still at the least 0.03.Phos is slightly elevated. Adding Chemipure Blue in the sump will help keep it in check