Water Changes (Cont.)
Water changes are typically done by using a hose to drain water out of an aquarium into a bucket, drain, or garden. There are several aquarium manufacturers that make a hose/gravel vacuum water change kit that can be connected to a faucet. These devices make water changes very easy.
The gravel vacuum is a popular device that was developed to clean the gravel of aquariums that used under gravel (UG) filtration common in the 1970's and 1980's. Since UG filters use the gravel in the aquarium as a particulate filter medium the gravel vacuum had become a common tool for doing water changes. While gravel vacuuming an aquarium that uses UG filtration is essential, it can be detrimental to fish health on an aquarium that does not use this type of filtration.
The top ¼ inch (5 mm) of aquarium substrate is heavily colonized with aerobic bacteria that are responsible for keeping the ammonia and nitrite levels at 0 ppm. When a gravel vacuum is used to clean the substrate of an aquarium that does not use an UG filter it upsets the ecological layers of the bed, and removes heavily colonized aerobic bacteria layer from being in contact with the water column. Typically this will cause nitrite levels to reach toxic levels three to four days after the substrate was vacuumed.
On a modern aquarium that does don't use UG filtration, the substrate should not be disturbed when using a gravel vacuum to pull water out of the aquarium. The gravel vacuum can be used to pull detritus off the top of the substrate if there are any spots in the aquarium where it accumulates. It should never be used to do a deep substrate cleaning.
There is a long running fallacy in the aquarium hobby that states that if you do not gravel vacuum the substrate, hydrogen sulfide will build up in the aquarium and kill your fish. Hydrogen sulfide exist in all natural substrates in freshwater and saltwater. It occurs in anaerobic layers of substrate. It will not build up in sufficient quantities to cause harm in the aquarium, as other aerobic bacteria in the aquarium will process it, much in the same way ammonia and nitrite are processed. If gravel vacuuming was required, you would not see all those beautiful planted aquarium photos on the Internet, in books, and in magazines.
It is recommended that you change as much water as possible when conducting a water change. 100% water change is acceptable as long as the new water is close to the pH, temperature, and TDS as the water you are replacing. Typically, you will want to lower the water level to the point where your fish just have enough water to swim, then fill it up with de-chlorinated water. The more water you can change out the greater the reduction in nitrate. When changing water using the hose method, a dechlorinator can be added directly to the aquarium while filling up the tank. Dechlorinator immediately neutralizes chlorine in the water.