exact water parameters arent as important as stable water parameters. I've kepts healthy tanks of dwarf gouramis and tetras in 8.2-8.4 water...those fish come from places with ph in the 6's...so unless youre going to filter thru peat or inject co2 or the like leave ph alone...can get you into trouble. Especially with chemicals to lower or raise the ph, these cause the ph to rise and fall which is extremely stressful to the fish. I'd say that if your ph is anywhere from low 6's to mid 8's you should be able to keep most fish healthy with just regular weekyl water changes.