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  1. #1

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    Default Water Changes - Whats your routine?

    0 Not allowed!
    Recently, the topic of water changes came up when discussing stress in relation to your fish tank.

    My arguement is that larger water changes (50%) every 2-3 weeks is less stressful on the fish community. The fish get stressed out with the activity in the tank, and you introduce new water (and new water perameters) into the tank less often.

    My buddy argues that smaller water changes more often are less stressful, 10-20% weekly.

    What is the opinion of the forum?
    55 Gallon Freshwater Tank (semi-planted) 48"x21"x13"

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  2. #2

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    western new york

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    1 Not allowed!
    50% weekly has never had any ill effects on my fish. Also I don't buy into this whole "water changes cause stress" thing. People's fish simply hide because there is activity in their tank. My fish like to play in the new water as it is being added to the tank. as long as the parameters and temperature of the tap water is close to the same as the tank water, there is not a problem. Bad parameters will stress fish a lot more than clean water will.

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    "Keeping fish for any period of time doesn't make you experienced if you're doing it wrong. What does, is acknowledging those mistakes and learning from them." ~Aeonflame
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  3. #3

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    0 Not allowed!
    Twice a week about 15-20%.

    If I want to do a water change without the fish noticing it I just disconnect the filter hose from the spraybar and hold it over a bucket. I usually syphon dirt from the lowest bits of thr tank at least once a week.

  4. #4

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    2 Not allowed!
    I researched this topic thoroughly for an article; at the risk of a very long post, here it the article text:

    Nothing is more important when it comes to aquarium maintenance than regular partial water changes. The adage “an ounce of prevention is worth a pound of cure” certainly applies here.

    One frequently reads of products that will reduce the need for water changes. Chemical media (carbon and such) may adsorb, absorb or change certain pollutants, but there is a finite limit to this and in some cases the pollutants return to the aquarium water in a different form that is still harmful. Some forms of bacteria will also release these adsorbed pollutants back into the water. And such chemical media frequently also adsorb beneficial nutrients which further worsens the state of the aquarium. Water changes also replenish essential substances such as minerals and ions. In the final analysis, there is no amount of filtration with any media that can duplicate the benefit of a regular partial water change. Everything that goes into an aquarium remains there in some form until we remove it.

    The water in the fish’s natural habitat is not static but constantly changing. There are water currents in streams and rivers; thermal currents in ponds and lakes; a regular influx of fresh water from rain and snow melt. Aside from all this, the ratio of fish to water volume is infinitely greater than what we maintain in any home aquarium. The toxins the fish expel—which include ammonia through respiration, solid excrement, urine, pheromones, and allomones—are regularly being dispersed. In nature, these substances are dealt with “naturally,” but the aquarium is a closed system and the operation of nature is greatly restricted. This “crud” is partially handled by filtration but no matter how much filtration you have on your aquarium, crud in some form continues to accumulate (Boruchowitz, 2009). The regular partial water change improves this situation considerably by injecting fresh water into the system as it removes a given quantity of the toxins. This is very important to the long-term health of the fish, and live plants will benefit too. The volume and frequency do somewhat depend upon the specifics of the aquarium, but as will be evident throughout this article, there can be no doubt whatsoever that the more water that is changed and the more frequently, the healthier will be the fish. And water stability is virtually impossible otherwise.

    An aquarium without regular water changes is like living in a sealed room without fresh air. Anyone who has worked in an air-sealed office building knows about this; regardless of the air conditioning system, it just is not the same as opening the window for fresh air. Like that air, the water in the aquarium becomes stale very quickly. Fish are constantly taking in water via osmosis, and they remove the minerals and expel the waste water along with any pollutants removed by their kidneys; an average-sized tetra produces 1/3 of its body weight in urine every day, so this quickly accumulates.

    Many aquarists wrongly assume that a rise in nitrates (or a drop in pH) is the trigger for a water change. But this is waiting too late; the health of the fish and the aquarium’s biology has already been compromised if it shows up in these tests. The whole idea behind regular partial water changes is to prevent this from occurring, by maintaining a truly stable biological system.

    1. Removing pollutants

    The natural bacterial processes that break down toxins in the aquarium do not remove them completely, but change them into another form that may be less but nonetheless still toxic; an example understood by most aquarists is the nitrification cycle whereby ammonia is changed into nitrite which is then changed into nitrate. More recent scientific studies have determined that nitrate levels above 20ppm are detrimental to most fish in our aquaria, and some will be negatively impacted even at 10ppm.

    And there are many others. Waste can be processed but it remains—until the water is changed.

    Pheromones and allomones. These are chemical substances released by fish, plants, and algae. Biology Online defines them thus:

    Pheromones: chemical substances which, when secreted by an individual into the environment, cause specific reactions in other individuals, usually of the same species. The substances relate only to multicellular organisms. This includes kairomones [these are released by flowers].

    Allomones are repellent pheromones that induce a behavioural or physiologic change in a member of another species that is of benefit to the producer.

    Just as hormones affect the body they are in, so pheromones and allomones released into the environment affect the bodies of other fish. These vary in function: some are used as communication between fish of the same species in a shoal—sometimes as a warning of danger; some initiate spawning behaviour between mates; some limit and even prevent growth of both the fish that releases them and other fish in the tank; some are warnings of aggression to other fish; and some indicate the fish is under stress.

    Reduction in microbial populations and their metabolites. Microbial population refers to all those microorganisms living in the aquarium water; included are pathogens—microorganisms such as a virus, bacterium, prion, or fungus, that causes disease. Maintaining fresher, more stable water by removing all these pollutants is one of the easiest ways to keep the fish healthy. Regular water changes can also help to keep algae from increasing.

    2. Water Stability

    This encompasses a number of factors. GH (general mineral hardness) and electrolytes must be replenished, and this requires either a water change or additives. Fish physiology will only function at its best under stable and appropriate levels, and these are important for the fish’s osmoregulation. Maintaining proper and stable pH and KH (carbonate hardness or Alkalinity) is also tied to regular water changes.

    DOC (dissolved organic carbon) accumulates, and while this can be assimilated by plants, it is easy for DOC to overwhelm the aquarium, particularly one without plants, and this has serious consequences for the fish.

    Nitrogenous substances in the water column such as ammonia and nitrite can be removed before they enter the nitrification cycle and thus help to keep nitrates lower. This is again more important in tanks without live plants. A rise in nitrates indicates a biological imbalance.

    Total dissolved solids (TDS) refers to the content of all organic and inorganic substances that are present in the water in a molecular, ionized or micro-granular suspended state. These build up from many sources: water conditioners and any substance affecting water chemistry; fish foods; organic matter; ions, minerals, salts and metals. As TDS increase, the ability of the water to hold oxygen decreases proportionally. The level of TDS also affects fish directly [see my article on stress for more detail]. TDS can only be removed by water changes.

    Replacing trace elements and minerals. These are important to the health of the fish, as well as the stability of the water chemistry. Over time they are used up or filtered out. If they aren't replaced, the pH of the water will drop. Furthermore, the lack of trace minerals will adversely affect the vigor and health of the fish and plants. Giving your fish fresh water regularly is akin to taking vitamins to remain strong and healthy.

    3. How to Do a Partial Water Change

    Stating the obvious, a percentage of water in the aquarium must be siphoned out and then replaced with fresh water. The substrate may or may not need to be cleaned during the removal of the tank water. In planted tanks, it is best to leave most of the substrate untouched; in non-planted tanks cleaning of the substrate is usually recommended to remove waste and other organics that in the absence of live plants will likely increase nitrates. [For more on this, see my article on Bacteria in the Freshwater Aquarium: ]

    Devices made for water changes allow cleaning (or vacuuming) of the substrate without pulling the substrate material out. These work well with any gravel substrate; with sand substrates, it is best to lightly vacuum only the top so that the sand is not also sucked out.

    Water changes in larger tanks are tedious using a water changer and a pail. The automatic “Python” apparatus that connects directly to a faucet is recommended.

    Water conditioner should be added either directly to the water if using a pail, or to the aquarium as the water begins to enter if using a “Python” device. Sufficient conditioner for the volume of water being changed is adequate in either situation. If the aquarium holds especially sensitive fish, increasing the amount of conditioner may be advisable. Although most manufacturers say the product is not harmful if overdosed, this is misleading; all conditioners increase the TDS (total dissolved solids) and they are chemicals.

    4. When not to do large water changes

    As the bio-filtration cycle operates, whereby Nitrosomonas bacteria convert ammonia (produced by the fish continually) into nitrite and then Nitrospira bacteria convert the nitrite into less harmful nitrate, a by-product is the production of acids. Normally the buffering capacity of the water keeps this from becoming problematical, and the regular water changes are part of this safety net. Without water changes for several weeks, the acids accumulate; the larger the fish or the more there are, the more acids. We call this “old tank syndrome,” and as this is gradual, the fish adapt with it. There comes a point when the buffering capacity in the water is maxed out, and the pH starts to fall, and if it drops to the low 6's the good bacteria can't function and ammonia starts to build. In acidic water ammonia ionizes into less toxic ammonium which allows the fish to survive. Everything continues to look OK from the outside. Then you finally do a water change, which in this situation can be deadly.

    The tap water pH will most probably be much higher than the pH of the tank water, and the more alkaline the tap water is, the worse will be the result. When half of the water in the tank is replaced with this fresh alkaline water, the pH in the tank rises and if it rises above pH 7 the ammonium in the tank water will change back into ammonia which is highly toxic, and the fish will succumb. The change in pH has a part to play as well, since the fish have to work extremely hard to readjust their internal pH to survive such a significant shift in the external pH, and this weakens them which only adds to the problem. It takes time for the Nitrosomonas bacteria to multiply to an adequate number to handle the sudden increase in ammonia, and similarly for the Nitrospira bacteria to handle the subsequent increase in nitrite. This mini-cycle is relatively short by comparison to a new tank, but it is just as stressful on the fish. In a thickly planted tank, where the pH is normally slightly acidic on purpose, the plants are able to take up much of the ammonium, which means the final result would not be quite as disastrous.


    Boruchowitz, David E. (2009), “Time for a Change: A Mathematical Investigation of Water Changes,” Tropical Fish Hobbyist, November 2009 (Part 1) and December 2009 (Part 2).

    Evans, Mark E. (2004), “The Ins and Outs of Osmosis,” Tropical Fish Hobbyist, February 2004.

    Muha, Laura (2006), “Fish Growth vs. Tank Size” in ‘The Skeptical Fishkeeper’ column, Tropical Fish Hobbyist, December 2006.

    Strohmeyer, Carl (2011), “Reasons for Water Changes,” American Aquarium Products website:

    “Growth Inhibiting Substance(s) of Fishes,” on the Wet Web Media at

    "Is Nitrate Toxic? A Study of Nitrate Toxicity" on the site.
    Last edited by Byron; 08-30-2013 at 07:57 PM.
    Byron Hosking, BMus, MA
    Vancouver, BC, Canada

    Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

  5. #5

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    0 Not allowed!
    When I'm raising discus and apisto fry, I will do up 80%+ wc's each day in the fry tanks. It benefits the fry great. My other fish tanks get around 30-40% wc each week at least. The adult discus tank gets a huge water change every 2 days.

  6. #6

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    0 Not allowed!
    Well said, Byron, the paragrapher. ;P I think you basically covered it all.

    To sum up what I do... Weekly 30-50% water changes. My fish also swim in the current of the new water and are truly curious about what the transparent magical force field is in the tank.

    That being said, if you leave a spray bar on and the water gets low enough, you do risk some stress in some fish from the several waterfalls that occurs. I've witnessed some flashing from SAEs when that occurs. You're supposed to turn off your filters anyway, but I'm lazy. ;P After noticing that, I'll probably return to my usual turning off of at least the canisters.
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  7. #7

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    0 Not allowed!
    I do approximate 50% weekly water changes on my 45 gallon, the only fish that seem to get a bit stressed are the peppered corys (they will all group together) but the remainder are fine. The tetras usually try to pick at the siphon because they see the left over food bits being removed and I've had my otos attach themselves to the siphon (never in a life time would expect that).

    In my 135 gallon when I do a water change the Adolfoi & Black corys will all come to the area where the fresh water is being added and swim up and down in stream just as happy as can be. They like it so much I would like to find a way to recreate the effect.

    I could never state the importance of the water changes as eloquently as Bryon but I know through testing that my pH, GH & KH remain stable and my nitrates remain below 10 ppm.

  8. #8

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    0 Not allowed!
    I do 40% weekly with a vac of the debris on the sand. Filters are cleaned monthly.
    75 gal - Smudge Spot Cories, Silvertip & Pristella Tetras, Scissortail & Red Tail Rasboras, Pearl Gourami, Black Kuhli Loaches, Whiptail Cats, Wild Caught BNP
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  9. #9

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    0 Not allowed!
    I change around 75% weekly, maybe a little more

    I have never seen my fish act any different or seam stressed by that. Been doing that on my current 90 gallon for about 4 years now
    If you take your time to do the research FIRST, you can successfully set-up and keep ANY type of aquarium with ease.
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  10. #10

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    0 Not allowed!
    I usually got with 50% once a week. Sometimes I'll do more. If the tank is looking a little more dirty than usual and I'm seeing more nematodes in my tank than usual than I'll do like an 80% water change and clean the gravel thoroughly. I do a 80%-90% water change at least once a month.
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