tropical fish water ph

Question
My 125 gallon tank has been set up since january. I have guppies,clowns,plecos,platties,silver dollars,cat fish and a shark in the tank. I have plants and rocks in the tank also. When I last checked the tank water everything was good (amonnia,nitrites and nitrates)but the ph was 6.0. I put two bottles of ph up in the tank over a week period and the ph won't rise above 6.6. I was trying to get 7.0 - 7.2 range. I have well water and do 15 gallon water changes every 7-10 days. I want to know why my ph doesn't want to go past 6.6.I also use a little aqarium salt in my water changes.

Answer
Hi Barry;

If the pH used to be up higher all the time there may be excess waste in the gravel making it drop and stay low. You need to make larger water changes and vacuum the gravel every week. A 25% water change in a 125 gallon would be about 30 gallons.

It's best to avoid using pH adjusters. They can cause fluctuations that are actually more harmful than the low pH. Do the larger water changes and also add bubbles with an air pump hooked to airstones. The additional oxygen will help release excess CO2 and the pH may gradually rise in response.  

At Your Service;
Chris Robbins