A simple but effective maintenance strategy every fishkeeper should know


When I started fishkeeping many years back, we hardly got any information about the proper care for our fish. Without the Internet then, our best source of information was the place where we got our fish from: the fish shop. Unfortunately, fish shops weren’t a reliable source of good and correct information. Most often than not, you ended up asking the shop caretakers for help, not the shop owner him or herself. The caretakers always have something to say about your concern and somehow, you ended up buying something to fix your problem. After all, it was their job to sell.

During the early years of fishkeeping in the Philippines, a lot of practices were developed which didn’t really make sense with today’s knowledge of fishkeeping. One of these involves cleaning the tank. For some reason, it was a common practice for fishkeepers to remove the fish, strip down the tank, scrub the glass panels, rinse the substrate, refill the tanks and return the fish. We know now that this is a terrible practice; but back then, that was what they told us to do.

From the terrible mistakes in the past of fishkeeping, the hobby was able to find a better solution. What works very well for today’s fishkeeper is the practice of doing partial water change (PWC). Simply put, PWC is removing 30% of the existing tank water and replacing it with new and fresh water. This is a simple maintenance practice that works well with the needs of the tank inhabitants and the fishkeeper as well.

PWC is oftentimes discussed and recommended in all fish groups, forums, and conversations. While it is really a very simple procedure, you should understand the knowledge behind this maintenance system to fully appreciate the results for you and your fish.


First of all, PWC is a maintenance procedure. It is not a filtration process. It will not make your tank water “clean,” but it will keep your water in good quality. So to fully appreciate PWC, your tank will have to have an adequate filter system that does the primary cleaning in your tank.

Your filter system, whatever that may be, keeps your tank clean because it has biological filter media which houses beneficial bacteria that processes organic matter in the water into less toxic materials. Owing to the process called the nitrogen cycle, beneficial bacteria thriving in the biological media convert decaying organic matter which the fish and other tank inhabitants excrete through their feces, urine, and other waste matters into less toxic materials: ammonia, nitrites, and nitrates.

While the beneficial bacteria are able to process ammonia and nitrite, they are not able to process nitrates. Good thing that nitrates are the least toxic of these three substances; however, in time, nitrates will accumulate at dangerous levels in the tank that can be poisonous to your fish.

This is where the PWC maintenance procedure comes in. The PWC process is what dilutes the amount of nitrates in the water. It may not rid the tank 100% of nitrates but it dilutes these to a point that the substance is not poisonous to fish.


Like I described earlier, the process involves removing 30% of the existing tank water and replacing it with new water. While it is really a simple process, there are a few things to remember when undertaking this procedure.

First, turn off the gadgets like the pump, heater, etc. You may keep the lights on so you can work in a well-lit environment and be able to see what you are doing. Just be sure the aquarium light does not hinder your movements and does not get wet and cause electrocution. Safety always comes first; be reminded that electricity and water is always a dangerous combination.

Second, prior to doing the actual water change, I recommend scrubbing the glass panels with a sponge to remove algae and any gunk on the glass panels. Remove stones, driftwood, and other decorations and rinse them separately in running water. Take a short break and let the solid wastes in the tank settle at the bottom.

After some time, during which the gunk has settled at the bottom, get your hose and siphon off the dirty water. After having started the siphon, suck out the solid gunk at the bottom of the tank. Make sure not to spook the fish when siphoning this off so that the fish do not scatter the gunk that has collected at the bottom.

Remember that the job requires us to remove just 30% of the water; after all the “P” in PWC is “partial.” There are many reasons why we are emphasizing “partial” in the water change process we are doing. If we partially replace the existing water with nitrate-free water, then we are partially removing “dirty water” and making that water “fresher.” So technically, we have improved the quality of existing tank water; no matter by how little, the tank water has still improved.

If we are to remove a huge amount of water, say 70%, then we would have significantly altered the water quality and probably its chemistry as well. With the fishes’ outer covering being osmotic, this sudden change in the quality and chemistry may have adverse effects on the tank inhabitants. This significant change can result in fish stress that can send them into a state of shock and possibly even kill them.

With this, it is important to note that we are merely doing a partial water change in this maintenance procedure. It is therefore best to make a mark in your tank about 1/3 below the distance from the water level. In truth, 30% is merely a safe estimate. This doesn’t mean doing a little less or a little more than 30% will be bad for the fish; rather, stay away from doing a lot more than 30% because it might do more harm than good.

Another thing to remember is to be careful while siphoning the water off because you may encounter some problems like:

  1. You may accidentally suck up and dispose of a small fish, and this can be a sorry loss.
  2. You could suck up a fish and injure or possibly kill it.
  3. Some fish are dangerous, and you might get bitten by a cichlid, flower horn, aba aba, wolf fish, or other ferocious fish. Depending on the species, this can merely be a painful surprise or you could lose a finger.
  4. Worse, you could get stung by a stingray, and this can be a very painful experience you will never forget. Or you could get stung by an electric eel, which can be life-threatening.
  5. Lastly one of the most common problems when doing PWC is when you lose control of the hose’s end, so that water is spilled all over the floor or carpet. Not only is this additional work for you in terms of drying off the floor, but you could also arouse the ire of others in the house.

After the water has lowered to the 30% mark, stop siphoning. It is now time to add fresh water. Some refill directly from the tap, while others prefer “aging” the water a few days before use. The latter, of course, is the better of the two options. This ensures that your water is chlorine-free and safer for your fish.


A single PWC will surely improve tank water quality, though not significantly. After all, we are merely diluting the amount of nitrates in the existing tank water. But to appreciate the benefits of PWC, this maintenance process should be done periodically. It is highly suggested to do this once a week, maybe twice a week at most.

If done periodically, this weekly maintenance schedule will eventually lower nitrate levels to a minimum and negate the harmful effects of nitrates on the fish. In the long haul, this simple maintenance strategy will ensure good water quality in your tank.

Like they say, a mile-long journey begins with a simple step…and with each simple step taken, eventually, you will have traversed your mile. With PWC, each simple improvement in water quality will eventually lead you to a tank with optimized water quality most suitable for your fish.


This appeared in Animal Scene’s February 2017 issue.