Instructions
Remove fish, plants, filter and all accessories from the aquarium. Pour out the water and the gravel.
Mix equal parts of water and vinegar in a spray bottle. Lemon or lime juice can be substituted for the vinegar if desired. The acid in the vinegar or juice will break down hard water stains.
Spray the vinegar solution on the hard water stains and rub with a cloth. Use a nylon scrubber on heavily stained areas. If an area is particularly stubborn, use a razor blade to scrape away the hard water buildup.
Rinse the cleaned aquarium thoroughly. This step is crucial because the acid in vinegar, lemon or lime juice can change the tank's PH and kill the fish.
Replace aquarium gravel, filter and accessories. Refill the aquarium with water and replace fish.
How to Remove Hard Water Stains From a Glass Aquarium
Nothing's more relaxing than watching colorful fish swim peacefully in a glass aquarium. But when hard water stains obscure the view, aquarium owners usually feel their stress levels rise. Hard water stains are caused by minerals in the water and do not harm the fish. Hard water stains in aquariums are inevitable, but cleaning them doesn't have to cause stress.