low PH-??

[fchaulk]

Problem with my PH being low

I have a 70gal tank with 65lbs of live rock and a 3" crushed coral bed. The tank has been running for 4 months. I use RO/DI water for water changes and the PH always drops everytime the water is changed. Been trying to change the water slowly to try and get the KH down a little. At least I think this is the right thing to do.

SG=1.024
PH=7.8
Calicum=400mg/l
KH = 280 mg/l , high
Ammonia , Nitrate & nitrite all are excellent

Any suggestions would be appreciated.

Thanks
Frank