What is Normal pH?

There is no "normal" pH that applies to all fish. Because fish originate in ponds, rivers, streams, lakes, and oceans that have different pH levels, their needs are different. Saltwater fish prefer an alkaline pH of 8.0 or above. Freshwater fish thrive in a range lower than that, somewhere between 5.5 and 7.5, depending on the specific species.

Keep in mind that pH is not static, it changes over time, in fact it even changes over the course of a single day. Typically it drops at night and rises during the daytime. The pH will change as new fish are added or removed, as water is added or changed, and as the biological processes change in the tank.

Preferred pH of Common Frewhater Fish
Angelfish 6.5 - 7.0
Clown Loach 6.0 - 6.5
Goldfish 7.0 - 7.5
Harlequin 6.0 - 6.5
Hachetfish 6.0 - 7.0
Neon Tetra 5.8 - 6.2
Plecostomus 5.0 - 7.0
Silver Dollar 6.0 - 7.0
Tiger Barb 6.0 - 6.5
Zebra Danio 6.5 - 7.0

How Important is pH?
Changes in the pH, especially sudden changes, can prove harmful or even fatal to fish . As the pH rises it increases the toxicity of chemicals such as ammonia. It is an important factor to monitor during the break-in of a new tank. pH changes are particularly hard on young and sick fish. In a number of species of fish, breeding occurs only within a specific pH range.

If you are planning a new aquarium it's wise to know the pH of your water source, so you know before hand if it is compatible. Some fish such as Discus, and certain cichlids, thrive in a very narrow ranges of pH which should be taken into consideration when setting up their aquarium.

When moving fish from one aquarium to another it is important to match the pH levels. Sudden changes in pH account for many fish losses that occur when fish are brought home from a pet shop. Water needs to be gradually mixed into fish bag from the aquarium.  Every 15 minutes add some water from the tank into the bag.  Keep bag and after about 1 hour fish should be ready for the move.  Do not dump the "bag water" into your aquarium.  Use a net to move the fish from the bag to the tank.  Neon tetras are particularly sensitive to sudden changes in pH, and can easily be shocked when moved, so pay extra attention with the new members to the family.

How Often Should I Check pH?
pH should be tested at least once a month, preferably once a week to allow for detection of trends before they become a problem. Test results should be kept in a log book for future reference. Remember that because pH can vary based on time of day, testing at different times of day can yield different results even though nothing is wrong. For this reason testing should take place the same time of day, preferably in the afternoon.

Any time there is a fish illness or death, the pH should be tested. If the tank is treated with medication, the pH should be checked when treatment is begun, on the final day of treatment, and again a week later.

It is also wise to test your water just before purchasing new fish. Check with the shop where you are purchasing the fish. It's important that the pH of water the fish is currently in is not significantly different than the pH of your water at home.

Should pH be Altered?
We recommend sticking to the saying of "if it's not broken, don't fix it". Don't spring to action simply because the textbook says the optimum pH for your fish is 6.4. and your water tests out at 6.0. As long as the pH is stable, and the fish show no signs of distress, it's best to leave the pH at it's natural level.  If pH needs to be altered, it has to be done over days.  A sudden change will shock the fish, ultimately killing them. There are digital pH monitors available which constantly check levels and can even control a CO2 canister to lower keep pH at specified levels (live plant aquariums).  Check back to see our live plant aquarium guide.