My tap water is at pH 7.2 - 8.2 so changing the water would not lower the pH.
Also, NO2 and NO3 readings are fine so because of that I would not need to change the water.
What I was wondering of is what are the factors the contribute to higher pH? I want to try to impact the root cause instead of fixing it temporarily.
Experienced people are trying to help you here and you really aren't listening. We can't help you if you don't listen. You are approaching the problem completely backwards.
Point #1: If your ammonia levels are too high,
you don't address that by artificially trying to manipulate the ammonia to put it in its safer form via pH changes. You address it by doing water changes to lower the ammonia level.
Period.
End of discussion.
Point #2: You are incorrect when you stated that you do not need to change the water because NO2 and NO3 levels are fine. The primary reason for doing water changes while cycling a tank are to keep
ammonia levels down. There will be a very brief window in the cycling process where ammonia is naturally decreasing and nitrite (NO2) is increasing; during that small window water changes might be needed due to NO2 levels. But in general, it is ammonia that causes the need for water changes, not anything else. (And of course, once a tank is fully cycled and both ammonia and nitrite are zero, then of course weekly PWC's are just to keep nitrates at acceptable levels.)
Point #3: It is rare for municipal water systems to put out tap water with a pH under 7.0 because many older houses still have copper pipes, and acidic water plus metal pipes is a bad combination. Because of this, it is very difficult if not impossible to set up an aquarium with a pH under 7 simply by using tap water. Borderline impossible, in fact. If you have a real, legitimate reason for needing an acidic-water tank (i.e. something to do with the particular species of fish you want, rather than this ammonia-manipulation idea), then you probably need to use a mix of tap water with bottled/RO (reverse osmosis) water, or perhaps even pure bottled/RO water, and put a substrate in your tank that buffers your tank in the acidic range (something like ADA Amazonia). Otherwise, you're simply not going to have an aquarium with an acidic pH. Not. gonna. happen.
Point #4: Have you tested your tap water pH after leaving it sit out overnight? I ask because tap water is under pressure to move it through the pipes. Pressure impacts the amount of dissolved gasses in the water, including dissolved CO2. Dissolved CO2 interacts with the carbonate buffers in the water and impacts pH. So often (almost always) the pH of your tap water immediately after getting it out of the tap will be different, sometimes radically different, from the pH of that same container of water after you have let it sit out all night long and re-establish its equilibrium with the atmosphere. Try that and see--I suspect that may be the reason you are seeing a difference in pH between your tap water & your tank water.
Point #5: When you say pH should go down in tanks without water changes, that is partially true and partially untrue. As fish waste (ammonia) goes through the nitrogen cycle, you have ammonia (NH3) being converted eventually to nitrate (NO3). As you can see, that means that three hydrogen ions eventually are "released" in the process. They go into your water. Hydrogen ions (H+)are of course acidic (the definition of acid). Now what normally happens of course is that because of the equilibrium with the carbonate buffers and atmospheric CO2, there is no impact on pH from this H+ release. Which is a good thing--it keeps your pH stable. However, if you go SOOO long without changing water (and thus replenishing your carbonate buffers) what will happen is eventually all of the free carbonates get used up. At that point, there is no longer anything buffering the free H+ and so it all stays in your tank in that form. This leads to a pH crash. And I mean crash. I had a tank where I let this happen by accident, my pH went from 7.6 to 6.4 in less than a week before I realized what had happened. It wiped out almost everything in there, including a pair of bright orange dwarf crayfish that I had paid about $75 for, as well as all of the babies they had recently had. Very very sad day.
So trust me, you absolutely positively do NOT want to see a pH drop as a result of lack of water changes. Because it won't be gradual, it will be massive and rapid and will probably send your tank occupants into pH shock like what happened with mine.
Point #6: Since you asked what raises pH, the normal answer is you only see significant pH rises if you use substrates that significantly buffer pH in the high range (aragonite, etc.) or crushed coral in the tank. Or tons & tons of a carbonate-based rocks like some forms of "Texas holey rock." But basically most people who want to have a high pH tank (for African cichlid tanks, Sulawesi shrimp tanks, etc.) achieve that by using an aragonite-based substrate, which can buffer pH anywhere from 7.8 to 8.4 or so.
So my final advice: keep ammonia (and nitrite) levels in check by doing water changes, wait until your cycle is fully completed & stable, and then measure your pH and decide what you want to do from there.
Good luck.
