I agree with Naja002, there might be some problem with you measuring your pH (i.e. perhaps you are using test strips, which are notoriously inaccurate). I find it unusual that your tap water has a pH of 8.8, but your aquarium water has a pH of 4.5.
Also, please do tell us how long your tank has been established. You say that you don't do water changes, and top off whenever the water gets too low. That may also be another problem, as DOCs will eventually build up and can potentially lower your pH.
__________________
Anthony
If you find my advice helpful, be sure to click the reputation button (it's on the left, and they look like a pair of scales)
|