7.8-8.0 first thing in the AM is actually not that low. Testing at that time is not really the best indication of pH as a rule either. That is when it is at it's lowest and is greatly affected by in tank and ambient CO2
. Midday (or midway through the photoperiod) is generally a good time to test. Be sure as well to test near to the same time of day each time you test to guage fluctuations.
As the day progresses, the algaes in the tank produce O2
counteracting the affects of the CO2
created at night. O2
raises the pH while CO2
supresses it. It is quite common to have a pH as low as 7.8 before lights on in the AM and 8.5 just before the lights go off at night.
Test at mid afternoon and see what you get. I would still post the alk
reading as Scuba suggested.