pH

For rainbow trout, a pH range of 6.5 to 8.0 is considered optimal, and adults can tolerate levels from 5.5 to 9.0. Natural reproduction is not successful in waters with pH less than 6. 

The pH level in our TIC tank must also be right for the nitrogen-fixing bacteria that will convert fish waste into less harmful compounds. Nitrosomonas (changes ammonia to nitrite) has an optimal pH between approx. 7.0 and 8.0. The optimum pH for Nitrobacter (changes nitrite to nitrate) is approx. 7.5 to 8.0.

pH is a measure of acidity of water. A pH reading of 7.0 is neutral. A pH higher than 7.0 is alkaline (basic), and a pH lower than 7.0 is acidic. Maintaining the aquarium at the proper pH ensures optimal water quality. The pH should be tested weekly, since natural materials in the aquarium (such as fish waste and uneaten food) can cause pH changes. 

(Ref. 1, Ref. 2, Mike Hewitt, EPCAMR, and Ref. 14)

(Ref. 2), (Ref. 4), (Ref. 5)