I am less than a week in on my first go at aquaponics after roughly three months of reading and research. This is a micro system by aquaponic standards; I selected this size to utilize hardware and resources we already had in an effort to learn about aquaponics on the cheap (relatively speaking). I am using a 30 gallon FT with two 15 gallon GB roughly 14'' wide x 23'' long x 12'' deep.

All connections were made, pump capabilities confirmed and plumbing tested prior to live start up. I have chosen to cycle with fish (40 feeder goldfish) and utilized a 4'' x 8'' dirty skimmer filter from the pet store to expedite the process. Stocking density is quite high and I plan to deal with this as needed (was expecting a mortality rate higher than zero!!!).

As of today my system pH has dropped to 7.0 from 7.6 which I believe is to be expected during cycling (ammonia is 0-0.25 ppm, nitrite is 0.25ppm and nitrate is 10ppm). I have added a few seedlings of romaine and leaf lettuce to the GBs. I am utilizing a Aerogarden with starter tray and plugs as a raft starter.

My question is regarding the pH and subsequent water adds due to evaporation, etc. My tap water has a pH of 8.0 and I am currently keeping a gallon pitcher on hand for adds, allowing sufficient time for off gassing of chlorine.
Should I try to adjust the pH in my add pitcher to target 7.0 or should I continue with the higher pH adds (perhaps a half gallon at a time) and allow the system to work out the pH? Also, is there a formula to determine the pH of a known sample after adding a known quantity at a different pH.

Thank you for any advice and apologies if this was posted in the wrong area.
Michael