Welcome to our forum.
As far as testing ... buy a CHEAP OTO test kit that tests for PH and chlorine/bromine and see what the reading is or go to your dealer and see what they test it at.
I already have a test kit- using the Taylor K2005 that I got from the good doctor......
7.8 although high isn't extremely high. Do you have some unbuffered MPS? If yes, through some of that in, it has a PH of about 4.Do you know what your calcium level is? Take a look at the Taylor watergram:With a Alk level of 70: At a Cal level of 80 and a water Temp of 104 - PH is above 7.8 and at 100 it's about 8.0. At a Cal level of 150 and a water temp of 104 - PH is 7.7 and at 100 it's slightly more. At a Cal level of 200 and a water Temp of 104 - PH is slightly under 1.5 and at 100 it's 7.6.I still believe your water is balanced and not to worry. PH will come down. I sometimes have a PH of 7.8 for a couple of weeks but I make sure my levels are within +/- 0.5 as stated by Taylor.
Anne,As you add bicarb, you'll be raising PH also. The good thing is that bicarb has a PH of 8.4 so that's the max the water can get.The higher you get in alkalinity you need to go down in PH because of your high calcium. Is your fill water naturally high in calcium?