Thanks guys, I calibrated the probe right before I put it in the sump a couple of weeks ago. I just bought 12 #7 and #10 packets so that I can calibrate on the first weekend of every month. I re calibrated by putting the probe directly into the packet and had the packet held with an algae clip in the water in the sump (for temp sake) and left it there for 25 mins. PH now reads 8.09, which is much better.