For some odd reason (plants? bubble curtain?) my Ph has fallen to very low levels. When I became aware of this I ran out and bought some ph up and added it to my tnak as directed. It says not to raise the Ph more than .2 in a 24hr period so can keep adding it every night at 6:30 until I get 7 again? And are my fishies gonna be ok? They seem alright now.

Have you measured your kh? That is the amount of buffers present in the water. The nitrifying bacteria need buffers for the process of converting ammonia to nitrite to nitrate. If these buffers are depleted you can have a pH crash.

If your kH is low, you can raise kh and pH by simply adding baking soda. Here is a link to Datagurus' calculator that determines how much is necessary.

pH and kh calculator