PH Problems - any tips?

[bluetang]

Hi guy and gals,
Ive recently set up a 125g tank in my front office at work. the tank has been up about 5 weeks now. I have almost got through my initial algea blooms but am having a problem with PH levels. they are low, at around 7.9 to 8.0 I cant seem to get it to rise. Ive been doing 20g water changes per week, but no change. I am also running a Calcium reactor on it with the efluent running at 6.9 I would have though that would stabilize it and bring it up
Any tips, product thoughts, or comments?

thanks
Rob