Is It Possible to Overdo Marine Aquarium Water Changes?

Water changes...the more, the merrier (within reason)

Water changes…the more, the merrier (within reason)

In a recent meandering conversation I had with my freshwater-pond-keeping brother-in-law, the question of water change volume and frequency was raised—specifically whether it’s stressful to the livestock if you perform them too frequently or change out too much water at once. My take on the question is that when it comes to water changes, the more, the merrier (within reason). With that said, I do need to qualify this position with a few important caveats.

Before I do, however, I should emphasize that this post is actually a thinly veiled attempt to get readers to join the conversation on the topic, so if you have any insights to share, please do so in the comment section below.

Anyhow, getting back to my caveats:

The parameters must match

With our beloved reef organisms hailing from one of the most stable environments on earth, it’s critical to avoid subjecting them to precipitous fluctuations in water parameters. Frequent water changes won’t be a source of stress if you’re always careful to match the temperature, salinity, pH, alkalinity, etc. of your replacement water to that of your display tank.

You’ve aged the replacement water

Of course, in order to ensure the parameters of your replacement water are a good match, it’s important to mix it up at least a day ahead of time, keep it circulating with a submersible pump or bubbling airstone, and heat it to the appropriate temperature. Don’t just mix up a bucketful of salt water and dump it into your tank. It takes a little time and vigorous water circulation to completely dissolve the sea salt and get all the parameters stabilized. It’s not uncommon to get slightly different measurements that need to be tweaked the following day.

You’ve controlled for tap-water impurities

Performing frequent water changes to reduce dissolved pollutants is counterproductive if you’re using unpurified tap water that contains a significant level of nitrate, phosphate, or some other contaminant to mix your replacement water. The obvious remedy here is to purify your source water via RO/DI before using it to mix salt water.

You’re not too disruptive

The simple act of siphoning or pumping water out of your tank and replacing it with clean water won’t bother your livestock to any significant degree. However, activities like vacuuming the substrate, rearranging rockwork, scraping algae, or otherwise tinkering around in the tank can be stressful if done too frequently. You don’t have to tackle these chores every time you perform a water change.

What about disrupting the biofilter with too-frequent water changes? Isn’t that a potential issue?
Remember, beneficial nitrifying bacteria colonize porous rock and other hard surfaces in the tank that are exposed to oxygen-rich water. You’re not going to reduce these colonies to any appreciable extent by siphoning out and replacing water.


If you enjoyed this post, subscribe to get our new posts in your email.
About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. I have a 37 gallon fowlr tank…I tried waiting two weeks between changes but my nitrates were getting high so now I do 5 gallons (bucket is prepped at least a day ahead) every week and my parameters stay within reason. I vacuum the sand every other, or every third change to keep the disruption to the fish at a minimum.

    I know this is a saltwater forum but on my 55 gallon freshwater (has approximately 29 fish), I do about 30 gallons every two weeks and my fish are no worse the wear for it.

    • Sounds like a good protocol, Bob. No worries mentioning the freshwater tank. After all, it was a freshwater guy who got the whole conversation started. Thanks for sharing!

  2. John Wilkins says

    There are so many different aquarium setups that you need to think it out for each unique setup. Size of tank, species, equipment, display-environment etc etc.
    I have cool marine tanks and collect my own specimens. Seaweed not Coral.
    I live by the sea and use natural seawater (100 feet frrom house)

    I jotted some ideas down recently .. thinking about one variable… water temperature control for my new project… a 7000L cool marine tank … my meandering thoughts may be of interest. Well.. posibly not to all you coral freaks.
    Some of this discussion diverges from the simple issue of water-changes.. but as we all know… no issue can be considered alone.

    The issue of Temperature fluctuation is a hugely complex one. In a Coral/Tropical Aquarium, strict temperature control is a vital issue and a variation of a couple of degrees away from the ideal is a recipe for failure.
    However, a cool marine aquarium with local fish and seaweeds and a complete absence of coral can be a completely different thing.
    You can still have a finicky cool marine aquarium if you select fussy species.
    On the other hand you can have a very forgiving aquarium if you select species from naturally changeable habitats (like estuarine or rock-pool).
    You might even want to mimic nature (biotope aquarium) and follow the natural environmental fluctuations.. either seasonal (heat of summer to cold of winter) or daily (tidal rock-pool). In these examples, actually creating temperature fluctuation might be a major goal and therefore a major challenge.
    My intention and current practice of Recreational Harvesting of specimens from a Cool Temperate Environment involves all sorts of options and experimentation. The knowledge base is not as well defined as in the highly popular Coral Aquarium field.
    So one basic requirement I aspire to is to understand all the factors influencing the temperature of my aquarium so I can manage the vagaries of my particular setup.
    My impression of the current cult of aquarium husbandry ….is of an endeavour which combines high tech ,high level science and a preference for strict control of multiple factors. However, the more you read, the more controversy actually exists concerning what works and what doesn’t work. Furthermore the age we live in is a speeding bullet train of changing knowledge and scientific expansion. In a hobby which puts a high price on equipment and aquarium inhabitants, it is understandable that there is a culture of “I must do it right or else I may be doomed”. This combined with an exhilerating forward momentum of tech and possibilities is an addictive mix.

    For my cool-marine project, it would be an attractive option (emotionally) to invest in a giant chiller and just stop worrying.. dial up my preferred temperature and let the chiller do its work.
    So why am I worrying about all the factors impacting on the temperature of my aquarium and trying to employ alternative ways of achieving temperature control.
    Well…. for one thing.. in all fields of knowledge you need to understand the whole in order to make true sense of the part.
    Perhaps at the end of this planning process I will employ a lot of strategies for temperature control PLUS employ a chiller. And hopefully that chiller will be used less often and at less expense.

    Current concept … avoid high tech heating/cooling technology (chillers, heater/chillers, geo-chilling/heating. …. see how it goes with the combination of sensible design/setup factors (below) plus our ambient climate. Let winter temps fall as they want. Hit standard Summer hot day with seabreeze through louvres … and rarer extreme Summer days (that don’t have seabreeze) with strong 240V house-fan on shower-head spray.

    My Target Temperature Range
    15-18C (59-65F)

    1. Impact of Water Changes

    Massive Water Changes

    (i) By definition these are most likely to be employed at greater intervals … ie weekly or fortnightly (rather than daily). Whereas they are great for dissolved waste and nitrate (etc) control.. massive water change may result in greater rapid-temperature-change at time of water change. Especially if there is a significant variation between aquarium and NSW holding tank ( I am planning a 20,000 L holding tank placed in the shade of trees in my garden). Both the aquarium and the holding tank can be subject to heating or cooling forces. Holding tank can be hit by summer sun or frigid winter nights, whereas the aquarium can be warmed by house-heating or nearby jacuzzi, protected from either winter-cooling or summer-sun by enclosing room, or even cooled by sea-breeze (with shower-head waterfall chiller coupling). Increasing the number of days between water changes allows increased time for temperature differentials to build up.
    This may be useful if you want to rapidly bring down an unexpectedly high-temperature aquarium eg after a very hot spell.
    It may be unwelcome if you have species which don’t like temperature fluctuations.

    Smaller Water Changes..
    Daily (or other short interval) smaller water changes are less effective at controlling dissolved waste and nitrate (etc) but are probably better for avoiding temperature fluctuations if you don’t want that.
    Small water changes via a bottom (Koi-style) bottom drain may be desireable for regular removal of solid wastes.

    Need to have a simple, reliable method of keeping track of temperature of both Aquarium and Holding Tank.
    What to measure … lots of data will be worthwhile collecting…
    a) Temperature of water drawn from bay week by week through the year
    b) Temperature of aquarium before and after each water change
    c) Diurnal variation of temperature of holding tank water
    d) Variation of water from bay depending on tide.
    e) Temperature of holding tank related to ambient/environmental temperature
    f) Temperature of water drawn from deep pipe-siting compared with temperature of shallow bay water especially in Summer

    Factors influencing temperatures.

    1. Use of an Aquarium Chiller in summer often considered a necessity for effective aquarium husbandry. It is practically impossible to chill the storage tank. So small water changes the only solution if there is any significant temperature differential..
    One alternative is a smaller secondary-holding tank which allows pre-cooling of that water before water-changes.. starting to sound too complicated.

    2. Where I draw water from in the bay in Summer. The shallow area closer to the shore heats up a lot making any storage water drawn from that exceptionally warm. It may be better to take the inlet pipe further out and/or more to the west (deeper water and more tidal influence). (? run pipe straight out south then curve to west). How far? Long ocean pipe to deeper water will mean cooler water to storage tank.
    This may alter the siting of the storage tank itself (and thus the piping to the aquarium)
    Perhaps site the storage tank to the south-west of the southern deck. Or if we envisage a long ocean pipe then it probably won’t make much of a difference where the holding tank is sited given the overall extent of piping.

    3. When draw water … incoming tide better as bringing cooler deep-water in.

    4. Reduce solar-warming of the storage tank. Keep in the shade. Light-coloured tank to reduce
    absorption and/or plant around it to further shade.

    5. Winter will introduce the reverse situation with the storage tank exposed to cool outside conditions and the Aquarium partially protected or even warmed by its siting inside a shelter which may even be heated.
    Another reason to use a chiller. If I chill water in aquarium in Winter to the same temperature as the storage tank .. then large water changes become a possibility.

    6. Temperature of Holding Tank … various factors
    (i) Its size… 20,000 litres will have enough thermal mass to avoid rapid swings during storage phase.
    (ii) Colour.. light colour absorbs less solar energy
    (iii) Sun exposure.. simply shade it
    (iv) Bury it?… let the earth act as a thermal moderator

    7. Size of water changes… say I plan to exchange 100% of aquarium volume per week… this might mean daily changes of 1000 litres. The holding tank will last maximum of 3 weeks. And because an empty tank can blow away in the wind, don’t let it fully drain.. so 2.5 weeks maximum.

    8. Effectiveness of Biofiltration elements …. even if theoretically relying on water changes as prime source of water maintainance, there will be a level of biofiltration happening anyway (large sand-filter, macroalgae).
    How effective this biofiltration proves to be will influence the need for and volume of water changes.

    9. Evaporative Cooling Using Shower-head sprays and fan/wind
    Jon Olav Bjørndal ” Evaporation cooling works very well for tropical aquariums, but not for cold water unfortunately. It is extremely cost effective, but you need to get rid of humidity and replace evaporated water.”
    Perhaps in my case the daily cool seabreeeze blowing at the aquarium will be effective for average summer conditions.

    Evaporative cooling by fans might only be required on those rare hot days when there is no sea-breeze….
    Commercial aquarium fans are designed for long-term use in hot climates on smaller tanks.
    As I may only need chilling/cooling on really hot days then the issues of enough air-flow to do the job (commercial quiet aquarium fans are designed for smaller aquariums) may be met with a nice strong house-fan as per the Majestic Aquarium’s video. On those few days.. who cares about the noise of a fan. And chuck in a bag of ice or two.

    • We definitely appreciate your thoughts here, John, and I think many other visitors will as well. Though still in their infancy, I suspect cool-water systems will eventually gain momentum as people look for a different sort of challenge. Keep us posted on your progress!

    • Stunning thoughts John…
      However if I happened to be just 100 feet from water…. I would solve all of my heating/cooling/seasonal regulating processes in one easy step…. An economical solution might I add… And using very OLD technology to the dismay of technocrats and science freaks…
      Yes I would do that without hesitating and get a water pump to permanently supply all and any tanks at my disposal !! And since I would only collect LOCAL specimens; the worries of filtrating adequately the returned water to it’s origins without risk of also rejecting invasive species would be non existent !!
      I could spend my days quietly gazing at the open sea on my back porch knowing everything was in total control !!
      🙂 A Great Day to all Salties
      Sylvain at

  3. Nice post John. Now I rarely do this but I kind of disagree with Jeff a little. I am also probably disagreeing with 18 million salt water aquarium owners but I think changing to much water can be detrimental to a system. Unless you are using natural sea water as you can change that every 8 minutes if you really don’t have a life, or a girlfriend.
    Artificial seawater is “not” sea water. It is fake seawater lacking multiple constituents of real seawater. Real seawater contains chemicals produced by algae, bacteria, coral, volcanoes, meteors and other things that have been there for millions of years and fish evolved with them. Many of those things are trace elements not measurable and not known if they are beneficial. (Real seawater also contains things of questionable value like wash water from Columbus underwear and Amelia Earhart’s shoes)
    There are a few reasons new tanks, with all new water look terrible. One thing of course is the lack of proper bacteria but the other is (IMO) the lack of those things I mentioned. No not the underwear and shoe thing, but the chemicals in NSW.
    Some of the water in my tank has been there from the 60s. Not much I assume, but some of it. There may even parts from Sputnik in there. Google it.

Leave a Reply to Jeff Kurtz Cancel reply