Not sure Im the best person to offer advice ( see the post on 'what is NH4 in chit chat!!)
But:
The easiest way I know to control ph is to keep the water in your tank at least moderately hard. If you have hard water in your taps then great, if not your into the murky waters of buffers, which basically make the PH more stable but some contain phosphates and cant be used with real plants, such as Aquarium pharmecuticals PH up and PH Down. So pick very carefully.
Bottom line:
If your fish have no problems in the water they are in now, then dont change it.
Fish waste and natural wood/plant matter in the tank lower PH over time, but your regular water changes counteract this just fine.
Even if the species is supposed to be kept in soft acid water ie Discus, cardinals etc etc, most will do fine in medium to hard water and in the case of domestic strains harder water is actualy preferable ie Angels (not Altums). The obsession with soft acid water is sometimes a requirement for breeding but all fish are much happier in stable water, not water where the PH and hardness goes up and down like a yo yo which is usually inevitable when you use buffers and PH correctors.
unless you are planning on getting Reverse Osmosis water, your best bet is acclimating fish slowly to your tap water and doing regular water changes, if you are planning on breeding south american or some west African fish then RO could be the only way to go. Consistency is the key...
Good Luck!
Ken