Ideal Alkalinity For Freshwater Aquarium. If alkalinity is below 50 mg/l, do not perform a water change until the alkalinity has been corrected. This certain level of alkalinity is similar to the alkalinity of the typical ocean surface.
Saltwater fish require total alkalinity in the aquarium to be 8.0 to 8.1. This is very different from the type of fish you intend to keep inside. The ideal tank setup for oscars.