acidity

So, 2 weeks ago I tried to get 3 ottos to keep company to the lonely one I keep (had 2, but one died about a month in and this one has been lonely ever since). All 3 died in days in the quarantine tank. I went back to the shop with water and pH test showed off the chart blue (api kit, same one...

I'm looking for some kind of monitoring system that will meassure eg. pH, nitrate, nitrite, temperature, tds etc. I have a TDS meter, digital thermometers in each tank and different chemical test sets to test for nitrate, nitrite and pH. I'd really like some kind of monitor or electronic tester...

Curious about what ways I can effectively and safely lower my pH. My tap water is around 7.4, trying to get my tank to anywhere under 7. I heard aging tap water is a good way to lower its pH, but after its in the tank and cycles for a bit with my aeration, wouldn't the PH just go back up...