maintaining proper pH

Question
Hi David,

We currently have a 30 gallon tank set up for about 3 months with 2 3" Discus, an Angelfish, and 5 neon tetras.  We have spring water and fill the tank with this water.  We make at least 25% water changes weekly and are trying to maintain a pH of 6.6 to 6.8.  Our spring water tests consistently at a pH of 6.0 and is soft.  We have been adding pH up to increase the pH of the tap water before adding it to the aquarium so as not to shock the fish.  However we cannot maintain the pH in the aquarium at the desired level.  The pH is consistently dropping and we are having to add pH increase on a regular basis.  We are testing for nitrates and nitrites and these levels are good.  Do you have any ideas of suggestions on why this may be happening and what we may be able to do correct this situation?  Also we use an Eheim canister filter.  Thanks.
Lori

Answer
aquarium water over time tends to drop in pH.  Because the water volume that is changed is not 100% (nor should it be), 75% of the water ages.  There is a simple and cost effective answer to your pH issue.  Add coral gravel to the tank. The ratio is one lb of coral gravel per ten gallons of water... but add the coral gravel in 1/2 pound lots and wait 24-48 hours to test the pH.  When you get a pH reading that is close to what you desire... then stop adding gravel and monitor the pH for a week or so.  hope this helps... dave