Hootchieman, you mention recent rains affecting your water-- if you're catching rainwater in a cistern I really envy you. In twenty years even the U.S. will be doing it.
The rainwater is even softer than your usual water. It dilutes the buffer, making your pH more flexible...
...but it doesn't drive the pH down very much, though the pH of rainwater is generally around 5.7. By contrast, the CO2 respired by fish and plankton etc is a major force depressing the pH. CO2 is also produced when plant and food detritus naturally degrades."Bio-acidification."
Three ways to counter this natural "bioacidification:"
1.Photosynthesis uses CO2 and raises unbuffered pH, so increase the lights (don't add more fertilizer).
2.Flush out your filter more often. (You probably have canisters, eh.)
3.Vacuum up all plant debris off the surface of your substrate. (don't disturb it though)
