The reason your ph is low is because your ALK is low and out of balance with CAL. Use the chemistry calculator that Reefer Rob suggested or this one
http://jdieck1.home.comcast.net/~jdieck1/chemcalc.html
Don't use PH buffers and dripping Kalk at this point will only raise your CAL and your CAL is too high right now but don't try to correct it, it will go down as you raise your ALK. Get a ALK buffer or read up on using baking soda as a ALK buffer
http://reefkeeping.com/issues/2006-02/rhf/index.php
Once your ALK and CAL are in balance your ph will come up and be in check, also adding ALK buffer will Raise your ph so add the ALK buffer very slowly
Good luck and I hope the links help
