When was the last time you calibrated the probe? They do tend to drift over time. The double junction ones are better at staying calibrated but will still drift too.
The thing that improved my ph the most has been my refugium. You said you have an algae reactor but I don’t think that would hold enough chaeto to have much of an impact on the ph. You’ve got a lot more fish than me but I’ve taken out my skimmer and just use the chaeto as my sole source of nutrient export and for ph (I don’t do water changes either).
I recalibrate my probe last week because my apex crashed and lost its memory.
The algae reactor is nowhere near big enough for this water volume. Its originally a biopellet reactor, I forget which one. I think aquamaxx. 5" diameter and 14" tall, approximately.
My current sump isn't configured for a fuge. I've considered switching to an external Skimmer and using that compartment for a fuge. Or making a baffle anemone using half of the return compartment but that's too small to really be useful.
I want to add a frag tank to this system after we move. I could put a refugium in line on the drain from the frag tank easily.
