Water Changes

by Frank M. Greco

Water changes are an essential part of maintaining the quality of the captive environment. Without them, particulate matter would accumulate in the substrate, pollutants such as nitrate, phosphate, and dissolved organic acids would increase to unhealthy levels, and the pH and alkalinity of the system would drop. Essential minor and trace elements would be depleted as well. Water changes remove the above mentioned (and other) pollutants while at the same time replenish diminished elements and restore both alkalinity and pH..

What's the best way to do a water change? By using a gravel cleaning siphon such as the Python No Spill Clean-n-Fill. These easy to use devices not only remove water from the system, but particulates from the gravel as well. These particulates, consisting of uneaten food, sloughed off mucus, fish waste and other assorted detritus will, over time, decay and degrade water quality. This usually results in a high concentration of nitrate (due to ammonification and nitrification) and phosphate (due to the release of phosphates in the organics). Low pH and alkalinity may also result due to the release of hydrogen ions (H+) during ammonification and nitrification. These ions aid in the depletion of the buffering capacity of the system(usually thought of in terms of OH-) especially in freshwater where the alkalinity reserve will be slight. Water changes with the gravel cleaner will remove these particulate and dissolved organics, thus aiding in the preservation of your alkalinity. Simply removing water from the system, while removing dissolved pollutants, does nothing to remove particulates in the gravel, and so is not as effective a method as using as gravel cleaning siphon.

Gravel cleaning will also keep the gravel "open", thus allowing for the free exchange of food and oxygen between the water and the bacteria growing on the gravel. This is especially important in systems utilizing undergravel filtration.

There is some debate regarding the gravel cleaning of planted aquaria. Many aquatic horticulturists feel that aggressive gravel cleaning will remove too much in the way of nutrients from the system, as well as damage plant roots. While I have not experienced this  with my own planted aquaria, which are gravel cleaned on a regular basis, perhaps it would pay to be careful when gravel cleaning a densely planted tank.

How often should water changes be done? Well, that depends on your water quality parameters and bioload. A chronically overstocked tank will require larger and more frequent water changes than will an under stocked tank. How much water can be changed at one time? Virtually all of it, should an emergency arise. However, some hobbyists may experience a temporary clouding of the water after doing large water changes. This is not harmful, and the cloudiness should disappear after a day or so. This is a rare occurrence, but you should be aware of it. Under normal conditions, though, you should not have to remove more than 25% at one time. Some folks perform 10% water changes weekly, while others, 25% once a month. How do you know which one is right for you? If after the water change, you do not notice a significant change in your water quality, try increasing the amount, frequency, or both. You can't hurt your fish by doing larger water changes. Oh...and don't worry about water changing during your tanks nitrogen cycle. Practical experience has shown me that water changing will not affect the cycling process at all, even if you do a 90% change daily.

O.K., now you are ready to do your water change. STOP!!! Before you remove ANY water from your system, check your tap water. Water that is being added back to the system should be close in temperature to that in the tank. While minor variations in temperature (± 2EF) will not harm the fish, but larger variations may bring about the onset of certain diseases such as Ich. This water should be free of chlorine, chloramine, heavy metals, and other pollutants. Using a "slimy" water conditioner and/or a chloramine remover will usually ensure that incoming water is satisfactory. These "slimy" conditioners usually neutralize chlorine and chelate small quantities of heavy metals such as copper and lead. In some agricultural or industrial areas, or if you are using untreated well water, you might also check for levels of nitrate and phosphate. If significant quantities of either of these are found, further water treatment will be required before use or the hobbyist should consider using reverse osmosis (RO) or deionized (DI) water (especially if a reef system is involved). One should also check the pH of incoming tap water. Due to the addition of chemicals to make our water safe to drink, the pH may be far more alkaline than the water in the tank. If this is the case in your area, you may need to buffer the pH down slightly before use. You don't need to match the pH levels exactly, and minor variations (±0.5 pH units) usually will not harm fish or invertebrates. Another tip: I do not advise the use of hot water to adjust temperature. Heavy metals such as copper and lead may be present in greater quantity in hot water (especially in areas where the water is naturally acidic). In addition, some older water heaters may leach toxic levels of zinc into the system. If you must use hot water, best to allow it to run for at least five minutes and check the copper level before use.

Water changes can go a long way to ensuring that your captive systems functions smoothly, and it is my hope that this short article has provided you with information on how to do one to the benefit of the animals.


First published in the newsletter of The Vancouver Aquatic Hobbyist Club