The Aquarium Water Change

Question: What is one of the best things you can do to ensure that you will be successful keeping freshwater and saltwater fish in your aquarium?

Answer: The partial water change of course. Performing regular partial water changes has numerous benefits and we’ll review them here.

Why do water changes?

The fish that we keep are living within an enclosed system and they continuously produce waste products as a result of various biological processes taking place within the fish tank such as:

  • Fish food that is eaten gets digested and waste products are generated, ammonia for instance.
  • Uneaten fish food that gets trapped in the substrate breaks down adding various elements to the water such as ammonia, nitrates and phosphates.
  • Fish are thought to be able to release pheromones and other biological products for mating and other purposes.
  • In saltwater aquariums, corals can engage in chemical warfare which is designed to harm competing corals.

Over time, as these waste products and other chemicals build up within the aquarium the quality of the water is diminished which can result in severe consequences for the tank inhabitants. One compound used to gauge the quality of the water is the Nitrate. In freshwater aquariums it can be a good rule of thumb to go by and can be a good indicator of accumulating Dissolved Organic Compounds (DOC). In heavily planted freshwater aquariums nitrates may not climb as high as those without aquarium plants. However, once nitrate levels start to climb past 20 – 40 ppm, it can be safe to assume that you should do a water change.

Saltwater hobbyists that are using large amounts of live rock or properly installed deep sand beds may not see high levels of nitrates due to the amount of denitrification happening within the live rock and in the deeper levels of the deep sand bed. Many hobbyists only change a small percentage of their saltwater aquarium water once per year! I don’t recommend this approach for the novice, since these same hobbyists are also usually adding supplements and dosing using calcium reactors to keep pH, alkalinity and calcium within acceptable levels. However, there are many trace elements that can be used up and skimmed off and these need to be replaced (in my opinion) via the routine parital water change.

The Replacement Water

It’s important to test your tap water to determine if you need to invest in a water filter unit. A pH, nitrate and phosphate test kit along with a Total Dissolved Solids (TDS) meter are recommended to get a good idea of how good your tap water is. If you’re lucky enough to get an annual water report from your water provider, read it carefully. Look for the levels on the aforementioned parameters.

For instance, if the water coming straight out of the tap contains nitrate levels at 20 ppm you may want to get a reverse osmosis (RO) water filter. Even those faucet mounted water filters that remove various larger grained substances are better than nothing at all and they are fairly inexpensive as far as water filters go. The faucet mounted filters also may remove chlorine and chloramine meaning that you may be able to add water without using any chemicals. Obviously, test to determine if your filter will remove these chemicals before using the water in your fish tank. The downside to using a faucet mounted filter is that you can’t use one of those fancy aquarium vacuums. You can still use the filtered water for top-offs in between water changes in your freshwater aquarium though.

For saltwater aquariums and reef tanks, you may want/need to invest in a Reverse Osmosis unit. You can make this aquarium RO filter unit even better by having Deionization as the final stage in the filtration process. These filters can remove most impurities from tap water. The downside is that RO units can produce a lot of waste water. Some produce as much as 4 or 5 gallons of waste water for every 1 gallon of pure water. You can always hook up the waste water line to run to a holding container that could be used to water your house plants and your yard. You’ll also need to install the RO unit which can be a time consuming task if you don’t already have an empty hole in your sink for the RO faucet. Have you ever tried to drill a hole in stainless steel? It’s not fun.

Aquarium Water Change Tips

Small frequent partial water changes are better than larger infrequent partial water changes for various reasons. The smaller water change will have less of an effect on the water parameters (pH, alkalinity, etc) and be less stressful for the fish and inverts in the aquarium. Larger infrequent changes of 50 percent or more can stress the fish tank inhabitants due to the possibly widely different water parameters between the tap water and the tank water.

The first thing you need to do is to turn off all electricity to the aquarium before working in and around it! Turing off the pumps could also make it easier on you when trying to remove that floating algae or to remove detritus from that under-gravel filter. Does anyone even use a UGF anymore?

Look into the aquarium vacuums that hook up directly to the sink such as the Python Aquarium Vacuum (pictured above). These make water changes a breeze. No more bending over and lifting heavy buckets and no more messes when trying to start the siphon on the vacuum! Freshwater aquarium keepers can also use it to replace water by twisting the nozzle on the vacuum to fill up the tank directly from the tap instead of pulling the water out. Add in the dechlorinator to the stream of fresh water entering the tank.

Saltwater aquarium keepers need to age the water for at least a day or two to let the mix completely dissolve and then test the salinity/specific gravity before putting the mixed saltwater into the tank. If you have a smaller tank this isn’t that big of a deal using 5 gallon buckets. But larger tanks may need larger holding vessels such as rubber trashcans or even a water softener holding tank for replacement aquarium water. An aquarium vacuum can also be handy here for removing old water from the aquarium. To add the new water from your holding vessel you can submerge a strong enough powerhead into the new water holding vessel (trash can or bucket), attach the properly sized rubber tubing and turn on the power head to push the new water into the tank or the sump.

Use the gravel vac to vacuum the substrate and remove any obvious signs of algae or detritus buildup first. Depending on the size of your fish tank, you may need to move quickly here. For my saltwater aquariums I try to skim the top surface of the sand. I don’t put the vac in too deeply into the sand, just the surface to remove any buildup of organic matter.

Water changes are perhaps one of the most laborious things to do as far as aquariums go, but I believe that they are extremely important. Make it a habit of doing it on Saturday mornings or Sunday evenings. After a water change, it can be very relaxing to just sit back and watch how your fish react to the clean water. They should be a little more active with more vigor and you can feel good knowing that you are properly caring for your fish!

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