API pH Up, 16 OZAPI pH UP pH adjuster raises pH levels in your aquarium to make water more alkaline when levels fall too low. pH is the measure of acidic or alkaline conditions in water, where a value of 7. 0 corresponds to a neutral pH, pH values about 7. 0 are considered alkaline, and pH values below 7. 0 are considered acidic. Different fish need different pH levels to be healthy, so it is important to test your water regularly to ensure pH levels fall where they