Every 5 days or so, my pH in the 55 gallon tank seems to drop massively. 5 days ago I set my pH at 7.0 and now it's down to 6.4. Is this normal for pH to drop that much that fast? Is 6.4 too low for the fish in that tank because they don't seem to mind? Can I leave it at 6.4? Because I'm going through buckets of these chemicals that alter pH. Does everyone here have to raise pH in a freshwater tank every few days or so? Any advice/comments? Thanks.