PH Levels of Fish

The pH scale was designed to measure the degree that a solution (in this case, the water in your aquarium) is acidic (0), neutral (7), or alkaline (14). In an aquarium, optimal pH will vary according to the species of fish you are keeping and the ecosystem you are attempting to replicate. Maintaining a consistent pH is more important than adhering to a perfectly optimal one, as rapid fluctuations in pH are extremely stressful for fish. However, forcing a fish to live in a pH far out of its natural range will cause stress and illness.

  1. Low, Acidic pH

    • Freshwater fish, which prefer water of a low, acidic pH (4.5 to 6.5), include South American discus and dwarf cichlids. Danios, barbs and loaches which hail from Southeast Asian rivers fall into this range, as their natural waters are between 6 and 6.5.

    Neutral pH

    • The majority of freshwater fish inhabit water with a pH from 6.5 to 7.5. This is the correct range for African tetras, catfish and African dwarf cichlids. This is the ideal pH for fish from India and Australia, such as spiny eels, gouramis, certain loaches, gobies, rainbowfish and Australian arowanas. This is also the range for South American piranhas, oscars, angelfish and hatchetfish. Goldfish do well in this range.

    High, Alkaline pH

    • Many cichlids from the Central American lakes, such as red devils, convicts, and blue dempseys, as well as the hundreds of species of African lake cichlids like mbuna and haps, thrive in alkaline water with a pH of 7.5 to 9. Mollies, guppies, and platies also prefer a more alkaline pH.

    Saltwater

    • Saltwater pH is usually between 8.0 and 8.4, varying only slightly according to ecosystem. Reef tanks tend to be a bit more sensitive than fish-only tanks, and should be close to 8.2 or 8.3.

    Brackish Water

    • Brackish water from salt ponds or mangrove swamps is generally 7.2 to 8.0. Brackish species, which do well almost anywhere within this pH range include knight or bumble bee gobies, puffers, orange chromides, celebes rainbows and tiger fish. Fish from slightly brackish water, such as spiny eels and kribensis, are best suited to a slightly acidic or neutral pH, while species which lean to the more marine end of the spectrum, like monos and scats, prefer more alkaline water conditions.

    Raising or Lowering pH

    • To raise the pH of your aquarium, use purified tap water rather than distilled or reverse-osmosis water. Other ways of raising pH include adding crushed coral or limestone to an aquarium's substrate or filters, or creating more water flow. To lower the pH of an aquarium, add peat to your substrate or filter, and use reverse-osmosis or distilled water in the tank. Driftwood in a tank also lowers pH. You may also purchase chemicals designed to raise or lower an aquarium's pH.