Just got done checking my nute tank. pH was stable all day today - still at 5.8
Did a little re-arranging in the tray. Moved 14 & 16 to pots of pellets and over to the "tall side" of the tray. Readjusted the lights since 8 had grown up almost into them - it may be a bit ugly, but it's still growing well. (Lights were moved up for the pictures)
Thanks to those who replied about using H2O2 with GH nutes. Since my pH was stable all day today I'm going to skip the H2O2 for a while and see how it goes.