Join Date: Nov 2007
Location: NYC & Long Island, NY
I would absolutely go with several small water changes, especially if someone else has been watching your tank for the last week. I'm assuming you measured Ammonia and nitrites, and everything is normal?
I would also consider the typical things that cause pH drop... driftwood, substrate, CO2. Either something is new, or perhaps you normally do water changes more often than once a week, which brings your tank water back up to neutral?
I've never heard of algae causing pH to drop. I have heard rumors of snail explosions causing pH to drop (due to buffering capacity of the water being sucked off to form snail shells). I really doubt it's the algae.