why's my pH so low??

[fishface]

i've pretty much finished cycling my tank...or so i think. ammonia is 0, nitrite is 0 and nitrate is barely perceptible but i was wondering why my pH is still at 7.7. is it as simple as boosting with baking soda or are there underlying issues? oh yah, check this out, i checked my ca with a hagen test kit and it measured just over 600 could this be possible? the salt i've been using is coralife marine grade scientific salt if that helps any.

can anyone spare me some knowledge here? please