First, a warning:
If you neglect your water changes for too long, the build-up of organic substances from fish waste and uneaten food will slowly reduce the pH. Most fish can adapt to this gradual change, but when you finally get around to cleaning your tank, the sudden rise in pH that will occur when you add fresh tap water may stress your fishâ€¦ possibly to death. If itâ€™s been a month or more since youâ€™ve done a water change, only replace about 10% of the water to start. Wait a few days, and then change another 10%. After your third 10% change, wait a week and then you can get into the recommended 25-50% a week routine without danger.
Frequent water changes help you avoid this problem by keeping your tankâ€™s water chemistry similar to that of your tap water. They also make the task quicker and easier. Imagine not cleaning your house for a month, versus picking up after yourself each day.
You will need:
A bucket: Make sure it is designated â€śfor aquarium use onlyâ€ť because even a tiny bit of soap residue can harm or kill your fish.
A siphon: an aquarium siphon has a â€śvacuumâ€ť end (which is fairly wide) that connects to a length of narrow tubing. This design prevents gravel from getting sucked up along with the debris and water. They are inexpensive and a variety of sizes should be available anywhere that sells fish or aquarium supplies. There are also siphons that extend from the tank to a sink or faucet, allowing you to do water changes without carrying buckets. Though more expensive, they are certainly worth the cost for those with large tanks or physical disabilities.
Dechlorinator: this is an additive that neutralizes the chlorine and chloramines, thus making your tap water safe for fish.
Step 1: Preparation
Unplug all filters and heaters. As the water drains from your tank, your filter will not be able to draw water through the intake tube and it will run dry, possibly damaging the equipment. Aquarium heaters should never be exposed to air while plugged in, as the heat will cause the glass housing to shatter, destroying the heater and causing an electrical hazard.
Step 2: Starting the Siphon
Place the siphon in the tank and maneuver it so that the vacuum end and most of the hose fill with water. Plug the end of the hose with your thumb and lower it into the bucket. If there was enough water in the hose, gravity will take over when you remove your thumb and water will flow from the aquarium into the bucket. Alternately, you can place the vacuum in the tank and suck on the end of the hose (like a straw) until water starts to flow through, then drop the hose into your bucket. This method is easier for some, but you risk getting a mouthful of aquarium water, so use caution. If you have a siphon that goes to your sink, follow the manufacturers directions.
Step 3: Vacuuming the gravel
Gently push the vacuum end of the siphon into the gravel and wiggle it around a bit. You will see debris from the bottom of the tank flowing through the siphon. Repeat this until you have cleaned all of the substrate or until youâ€™ve removed 25-50% of the water, whichever comes first. If you werenâ€™t able to clean the entire tank, just continue where you left off the next time you do a water change. Be sure to move tank decorations and vacuum under them, as debris seems to get trapped in those areas. Remember to keep an eye on your bucket so that it doesnâ€™t overflow. Hint: used aquarium water is great for houseplants because itâ€™s full of natural fertilizer!
Step 4: Cleaning the tank
Now is a good time to wipe nuisance algae off the sides of your aquarium. If you have an acrylic tank, only use scrub pads designated as safe for acrylic (these are available at most fish supply stores). Glass tanks donâ€™t scratch as easily and Iâ€™ve even used Scotch pads on mineâ€¦ just be sure that theyâ€™ve never had soap or other chemicals on them!
Step 5: Refilling the tank
Replace any decorations youâ€™ve disturbed while the water level is low. Fill your bucket with fresh water the same temperature as your aquarium water (you can use a thermometer, but even your hand can be fairly accurate). Add dechlorinator to the bucket, following the manufacturers instructions. I like to use a pitcher to move water from the bucket to the tank because I find that it disturbs the tank less and I donâ€™t spill as much. Repeat this until the tank is filled to the appropriate level.
Step 6: Finishing up
If you have a filter that hangs on the back of your tank, make sure that it is primed (full of water) and then plug it in. Once your filter is working properly, you can plug your heater back in, wipe the water spots off of the outside of the glass, and youâ€™re all set! It might take a couple of tries to get a system worked out, but itâ€™ll go quickly once you get the hang of it. A ten or twenty gallon tank shouldnâ€™t take more than fifteen minutes. If it gives you any idea, I can do all six of mine (totaling 154 gallons) in under an hour.