pH adjustment trouble

Feb 13, 2011
South Carolina
I have been testing and trying to adjust the ph in my aquarium since i set it up four weeks ago. It is a 30g hex with live plants.

The pH of my tap water is around 7.5 and this is where my tank has been the whole time. I have been using the API master test kit to test for pH, ammonia, nitrites and nitrates. I also have API pH up and pH down to adjust pH levels.

Upon first testing my tank water and finding a level of 7.5, and my fish prefer 6.5-7.0 I added the recomended amount pH down to bring the level close to desired. After leting the tank settle for 24 hours I tested again and came up with 7.5pH. I added the recomended dose again on the second day and let rest for 24 hours. When I tested again I still had 7.5. Not wanting to add too much i let the tank sit for a week. I tested again, 7.5pH, and added more pH down. I have done this several times in the four weeks this tank has been in opperation and no changes.

Does anybody have ideas or sujestions on why my tank is not changing pH?
NH3/NH4, NO2- and NO3- are all 0ppm

30g planted hex
1 Dwarf Gourami
3 Neon Tetra
3 Glowlight Tetra
1 Julii Cory Cat