Since it is happening on multiple tanks, not 100% sure yet, the water changes are my buffer while I try to figure it out. Ph right out of the tap is over 7.5, I'm running it aerated overnight right now to see if it drops a lot. Might be too Mapuche decaying plant matter, might also be the gravel, doing some aeration tests now. Might also be some of the drift wood, I hear oak will drop your ph like crazy. Lots of variables right now.