I have been having the same problem starting a few days ago,ever since I bought a piece of bogwood and did not let it soak long enough and put it in my tank. I noticed one of my fish hiding out (unusual for him) and got a little suspicious. I tested my water perimeters and found that my ph level had dropped from 6.6 to 6.2 and freaked. I did 4 gal. water changes in my 29 gal. tank to try to raise up the ph (the ph from the tap is 7.2) it did a little to 6.4 then I left it. When I went to check it again the ph level dropped. I did not do research on bogwood and was unaware it lowered the ph in the water as was told to me by the person that worked at the lfs. So I took it out,did water changes (same as before) the ph went up a little and I left it and again. Tested once more and there was no improvement, it dropped again. So more water changes and more testing and to no avail the same result. Anyway tonight I tested again and the ph result was a darker yellow than what was on the chart. Now I am really freaking out,so I called the lfs again and the person said to take out everything that could possibly cause the level to continue to drop (which happened to be for me a couple small pieces of bogwood I had in the tank since cycling and my lava rocks), put them in seperate containers and let them soak in dechlorinated water for a couple hours and test the water to see if that may be causing the problem. He says to try to find the source before trying to fix the problem. So that is what I am doing now. My findings at this point when I tested the seperate containers the ph level dropped from 7.2 to 7.0 in an hour or so. I pray that it is what it is so I can resolve the problem without adding anything into my tank that I don't have to and that my fish will survive another night. I have 5 zebra danios,a male + 2 female gouramis,and 2 peacock gudgeons in my tank so far(my 2 bolivian rams are in quarenteen). The rest of my water perameters were normal at 79 degrees. Hope that my novel helped a little and rest assured you are not alone dealing with this ugliness right now.