well they natural come from accidic water, but personaly i would keep it mroe around 7(nutral). the problum is most testers only go to 6, so it could be even lower u jsut dont kno. also if ur water is too acidic the bacteria that breaks down ammonia and nitrite, can stop functioning and breaking it down(no buffer). so i would try and keep it closer to 7. test your tap water i would assume its higher then 6. may jsut need to do soem watcher changes, or add buffer like calcium carbanate. also wood will make your ph drop incase u have that in there.