Following these guidelines will keep your fish feeling fine. You should replace about 10 to 20 percent of the water in your aquarium every one to three weeks or so. For example, if you have a 50 gallon tank, you need to regularly remove and add back about 5 to 10 gallons.

The introduction of new water helps maintain stable conditions and mimics natural conditions. It also keeps nitrate concentrations at reasonable and safe levels. There are many ways to change your aquarium's water, but we recommend using a gravel vacuum to siphon out water and clean detritus from your gravel at the same time.

To use a gravel vac, you'll need a large bucket to hold the old tank water. Move the suction end of the gravel vac through the tank's gravel, loosening and sucking up all the detritus caught between the little stones. Empty the water the gravel vac siphons from the tank into the bucket and continue this process until the desired amount of tank water has been emptied.

Once you've used or dumped the old water, use the same bucket to measure out the new water. When using the bucket method of water changes, don't replace the old water with water straight out of your tap. You'll need to treat it first. Make sure the temperature of the replacement water is as close to the temperature in your fish tank as possible. Do that by blending hot and cold water from the faucet.
To make sure no harmful chlorine gets into your aquarium, add dechlorinating drops or tablets to the new water, following the manufacturer's directions. Pour the new water into the tank very slowly. If someone is available to help, have your assistant cup their hands on the surface of the aquarium water while you pour the water from the bucket into his or her hands. You'll need to repeat this process until you've replaced the necessary amount of water.

If you'd like to avoid the repetition and potential mess of this task and use the water directly from the tap, there is an elegant gadget called the Python No Spill Clean and Fill, which works by utilizing your faucet's own water pressure. It comes with either 25 or 50 feet of tubing, so all you have to do is attach the correct end to your kitchen sink faucet, turn on the water to the desired temperature, place the suction end in the tank, give the nozzle one twist and bang, you have suction and the tank is draining.

On the tank end of the Python No Spill Clean and Fill is a device like the gravel vac that lets you clean the bottom of the tank as you siphon off water. When you have drained enough, turn off the faucet, remove the hose from the tank and add dechlorinated water.

It's a good idea to test the pH of the water in your aquarium after you've completed a water change. You should have a pH test kit, which will show you the relative acidity or alkalinity of the tank's water. These kits are easy to use. Just read the manufacturer's instructions.

Do research on the pH necessary for your particular species of fish. A pH reading of between 6.8 and 7.2 is good for most fish. However, every species has its ideal pH level. Neon tetras and barbs for instance, like their pH level slightly acidic, in the mid-sixes. But, many cichlids want their water hard and alkaline, in the upper-seven range.

If the pH level in your tank is not what it should be after a water change, add a few drops of the appropriate agent to raise or lower the pH level to the proper range. If you find the pH remains within an acceptable range consistently after water changes, you can do the tests less often.