Your tank would have to be around pH 6 to start dissolving any bound phosphate. Needless to say, I don't think your tanks' inhabitants would be doing very well at that pH.
A pH around 8.0 is nothing to worry about, but if you're
that concerned, the CO2 released from human and animal respiration impacts pH by lowering it. The amount of CO2 in a home is often significantly higher in the winter months when windows and doors are kept closed. Better air exchange near the sump can make a big difference as well as airing the house out a few times per week by opening a couple windows and allowing a breeze to go through for awhile. Try this before messing around with the pH directly. If you're messing around with the pH directly you're very likely casing pH swings which stress the inhabitants more by leaps and bounds.