Fish-proofing an aquarium is no more than making sure everything you place into the tank such as cleaners, water, substrates and decorations are safe and acceptable for your fish.

Before you first fill your aquarium with water, give it a good cleaning using mild cleansers and disinfectants. Using a mild bleach solution will rid it of any unwanted bacteria, but make sure you rinse it very thoroughly afterwards and allow the tank to dry before filling it. If you clean the tank without draining it, use an algae scrubber or magnetic scraper to clean the algae off the walls, and use a siphon to clean the bottom of the tank.

Another issue for keeping your tank fish-proof is proper maintenance of the water. You should know what water chemistry the fish you are planning to purchase require. If you are planning to use tap water, you need to test the pH, chlorine, general hardness (GH) and ammonia/nitrite levels. If the levels do not match what you are going to need, you'll have to purchase chemicals to allow you to establish and maintain the proper levels.

Any level of chlorine in your water above 0.004 ppm (parts per million) will kill your fish. When chlorine from your tap water mixes with ammonia from the fishes' waste, chloramine is produced. It remains in the water for a very long time and is known to be hazardous to both fish and plants. Use a fish-safe chlorine remover.

Your water chemistry has many components:

• Ammonia: fish waste, hazardous to fish and the first step in the Nitrogen Cycle
• Nitrites: result of the first step in the Nitrogen Cycle, still harmful to your fish
• Nitrates: final result of the Nitrogen Cycle, harmful in high quantities
• pH: the acidic/basic level of your water. 7.0 is neutral; higher levels are basic (also known as alkaline) and lower levels are acidic
• GH: refers to the dissolved concentration of magnesium and calcium present in your water (how "soft" or "hard" the water is)
• KH: "carbonate hardness," which refers to the quantity of carbonates and bicarbonates in your water.