Ending Death Row

Question
35 gallon tank with 32 inches of fish made up of Molies, Tetras, Bristle Nose, and Catfish.  The Molies are new, most others are established.  Tank has been set up for at least a year.  

For the life of me I can not keep the Ph near 7.0.  My tap water runs around 7.2-7.6, but my aquarium is 6.0.

6 months ago the Ph was high.  The local store recommended bogwood. That seemed to help, some.  I ended up using Proper Ph 7.0 from API.  Things were stable for a few months. I had removed the bogwood and stopped using Proper Ph 7.0.  

After adding the catfish, I included some life plants (I'm no longer using Proper Ph 7.0 from API, which is not good with plants).  Since then my aquarium has slowly gone acidic, measuring in around 6.0.  I am doing frequent partial water changes (My tap water is 7.2-7.5), but it is not having any effect.  

Although the Ph is low, it appears to be stable.  So far the fish appear to be healthy, but loosing some color.  Any advise on controlling the Ph would be appreciated.   I don't understand what is causing it to go acidic.  I plan on continuing with frequent water changes, for now.

Answer
Well, first I would tell you that your fish, being very hardy fish, are not picky at all about the pH. Yes, some pet stores will tell you to fix it but in the end hardy fish simply just dont care. Next, using any pH stabilizer will work great for a while but is never a permanent change and just adds mean little chemicals into the water which are not natural. Adding more plants might help you control your water or at least make it more natural for the fish. I would also not be concerned about the plants requirements of pH as I am sure the plant you got is hardy, as most are. In the end, I would aviod using chemical pH fixers unless you have very fragile or picky fish, which you do not right now. Next, while your tap water is a good pH it is regulated by chemicals basically like your pH for the tank, so in the end the pH does not stay and tends to go down. Bottom line is that unless your fish are showing signs of stress, dont worry about it unless you get picky or fragile fish. There should be no reason why your fish cannot have a happy and healthy life living just as they are in the 6.0 pH. Also, only change the water in an established tank every two or three weeks and only change aroud 15% of it. This will help provide a stable environment for the fish. If you continue to move the pH with water changes the fish may not respond well but keeping the pH where it falls, low or high, the fish have the chance to get used to it. I have three large tanks right now that have so called "bad" pH but the fish are thriving because they are hardy fish and dont really care. I hope this helps.