PH Testing Strips 25pkPH is the measure of the acidity of water. In order for fish to thrive, it is important to maintain aquariums pH at a level similar to their natural habitat. Most freshwater fish do best at a ph range of 6.8 - 7.5. Saltwater fish should be kept at a range of 8.2 - 8.4. This kit contains 25-test strips, easy to read instructions, and information to correct unsafe water conditions. For fresh and saltwater aquariums.