At Dallas Aquarium Experts we believe water changes are the most important aspect of aquarium maintenance. Only diet ties with how important water changes are, and they are equally important. You can provide the best food or water quality, but if one is lacking it can undo the highest quality in the other.
There are many vital things that water changes and regular aquarium maintenance can do for the aquarium. Regularly scheduled water changes can actually help save money when it comes to filtration since they can make the use of carbon filtration completely unnecessary. Nothing, absolutely nothing, can make up for a lack of water changes done while performing aquarium service. Filtration can’t do it. Special additives and special types of filtration can’t do it, nothing can replace water changes done while serving an aquarium.
It is important to understand exactly what filtration and water changes do so that you understand the difference. Filters do two main things. First is that they provide a place for the bacteria that consume ammonia and nitrite to grow. The surfaces of bio-medias and the flow of the filter create the perfect submerged habitat for these nitrifying bacteria. The other main function is to physically collect debris and particulates from the water column for the aquarist to remove during regularly scheduled aquarium maintenance at which time the filter media is replaced. It is vital to perform filter maintenance, regardless of the type or brand of filter being used or whether the flow is reduced or not. Water changes maintain water quality long-term.
The problem with water changes is that their results are long-term. Many people only see short-term. So if someone stops doing water changes or cuts back drastically (like only doing water changes once every four weeks) they may not see any major difference. The reason is that the problems related to lack of water changes, cause short-term are very subtle. Many people feel it is best to leave well enough alone and not fix what isn’t broken. This idea leads to neglect and the aquarium will suffer.
When inadequate aquarium maintenance or no water changes are done the tank appear to do well. The fish will still be alert and swimming, they will still have colors, and they will still eat. This can go on for a few years. What I have seen happen under these circumstances is called old tank syndrome. This is when the water quality has gotten so bad that all of a sudden effectively every fish in the tank gets sick. I have seen this happen a few times, killing 90-95% of the fish. A sign that this situation may be occurring before it actually kills everything is when new fish are added. Usually a neglected tank’s chemistry will change over time. The pH will drop along with hardness, the water quality is low, and together these can prove fatal to new fish. The fish that experienced it slowly acclimated to the changing water as it slowly happened. New fish are acclimated in less than an hour. This sudden change can shock new fish, resulting in their death with no symptoms of any problems.
Water changes do two things simultaneously. Most importantly they remove all the bad things that build up in the aquarium over time. These things include nitrate, phosphate, growth inhibiting hormones that many if not most fish give off, dissolved organic compounds, and other things. The other things are at least as important, we just don’t have test kits for them (except phosphate). The other major function of water changes is to bring in good things that are used up over time. The end result of all the biological activity in an aquarium is acidification. This uses up the KH in the water. As the KH is used up the pH will decrease. Eventually the pH will crash. There are many other vital minerals and trace elements needed that are replenished with water changes during aquarium maintenance.
Water changes also have a massive impact on stocking. It is an error to discuss stocking without addressing water changes and water quality. Discussing stocking based on tank size alone is not different from simply going by the very common one inch per gallon’ type guides. Experiments have shown that it is the water quality, not tank volume that stunts fish. The volume of the tank has a minimal impact on water quality.
How much, how often:
Water changes should be done on a minimum bi-weekly basis during your regular aquarium service. This frequency gives little time for the chemistry of the aquarium to change significantly compared to the tap water in a freshwater aquarium. Over time the chemistry in an aquarium changes and allowing too much time between water changes allows the tank’s water chemistry to change too much, this means that a larger water change will change the tank’s chemistry too much and stress or even shock fish. The amount changed at each water change should be whatever is needed to keep the nitrate concentration under 20ppm. This means that if a weekly water change of 25% doesn’t keep the nitrate concentration under 20ppm then the amount of water changed every week needs to be increased. Any time the size of the water change is changed it should be done slowly. Smaller water changes allow for more error than larger water changes. For example, if the temperature is not perfect for a 25% water change it may not cause any problems. The same temperature difference with a 50% water change could severely stress the fish.
Water changes can prevent and fix almost any problem:
Water changes are one of the most powerful ways to prevent and treat almost all problems that an aquarist is like to encounter. A healthy water change schedule performed during regular aquarium service can prevent most of the problems an aquarist might otherwise experience. In my experience the health issues that arise in well maintained tanks is almost nothing compared to those that are more neglected, including monthly water changes.
In addition, water changes alone are frequently all that is needed to fix most problems that may arise. Increasing the frequency of water changes when problems do arise may be the only action the aquarist needs to take when fish are stressed (lethargic, clamped fins, refusing to eat, etc.). It is also all that is needed in many cases of a variety of diseases. I have seen case after case of ich, bacterial infections, fungal infections, and others fixed by increasing the frequency of water changes alone, no medications used at all. It is also the main issue when algae problems arise. More or larger water changes are frequently the only change needed to fix algae problems.