You may not like the answer, but it depends on the fish chosen. Most get by with a low of 6.5 but some are more comfortable with a little more alkaline, up to 7.5. read more
Many freshwater community fish thrive in a broad pH range between slightly acidic (6.5) to slightly alkalic (7.5). To provide their ideal water conditions, you must learn how to make adjustments to your aquarium water using pH conditioners. read more