# Do water changes kill fish?



## Knight~Ryder (Dec 2, 2007)

Q: It's a commonly heard, but not completely accurate story, that water changes are bad and will kill your aquarium fish. How did the story start, and is there any truth in it? Like many misconceptions, there is a kernel of truth behind the tale. 


A: As someone who has worked in the fish department at PETsMART for the past 5 years and has kept aquariums for nearly 10 years, your article definately echoes what I tell customers at my store on a regular bases; water changes are the best type of filtration you can ever give your fish. Think about it: In nature, streams carry away old, waste-laden water and replace it with fresh clean, waste-free water almost every second; this only happens in an aquarium when the fishkeeper decides to do a water change. A lot of people mistakenly believe that topping off evaporated water is doing a water change when in reality they’re not really “changing” anything.

They don’t seem to realize that the water their fish swim in isn’t harmful, it’s the waste IN the water that is and when that water evaporates that waste is left behind. A filter does help but aside from providing a home for benificial bacteria, a filter is more akin to sweeping things under the rug rather than removing them from the tank. What fishkeepers have to realize is that the accumulated sludge still leeches by-products, particularly nitrate back into the water which then has to be removed via water changes. Changing water has several essential functions: It removes wastes, boosts fishes immune system, is the biggest contributor to fish growth and development, cuts down on algae, and saves money on the costs of filter cartridges since you’re doing half the work of removing sludge that would otherwise clog filter cartridges. 

Since water changes remove waste from the tank, you can appropriately think of it as flushing your fishe’s toilet. What’s more, that “waste” water doesn’t have to go to waste: Fish manure makes an excellent natural fertilizer for potted plants, gardens, or grass.
There’s no such thing of doing to many water changes, I myself perform 25-50% water changes on several of my tanks 2 or more times a week with stunning results! And some fish breeders perform 90% or so water changes several times a day! (grant it, they don’t use filtration). For the average hobbyist, I usually recommend at LEAST 10-15% water changes every week rather than the 25% water changes many sources recommend every month. Not that this is bad, but consider how much faster and easier it is to get to the gunk before it has a chance to build up rather than wait a month and then spend perhapse an hour or more endlessly siphoning a month’s load of mulm from the bottom of the tank; I usually have much better results doing weekly water changes but everybodys different, these are just suggestions. What matters in the long run is that you perform the water changes, no matter how you decide to do it. 

Source: http://freshaquarium.about.com/b/2006/07/26/do-water-changes-kill-fish.htm


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## dm800 (Nov 3, 2007)

While we are on the subject of water changes, I thought I'd ask this to make sure I have been doing it right. I typically shove the end of the vac into the gravel and see a lot of the gunk get sucked out that was in the gravel. The gravel did not look dirty, so it must have filtered its way down into the gravel. Anyways, by the time I get the entire bottom of my 10 gallon tank vacuumed, I end up sucking up at least 50% of the water. So I don't see how it is possible to do a 10-20% water change, unless I am doing it too deep. I was just reading some info on plants, and saw where it said not to push into the gravel because it could damage the roots. Maybe thats why my plants slowly die off, but I will save that for another post. But for people that have a bunch of plants in the tank, how do they vacuum the bottom with all those plants? Do they just skim the top of the gravel around them? Doesn't all the gunk build up under the gravel eventually?


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## Obsidian (May 20, 2007)

The gunk is called mulm. Yes it goes down into the gravel like you noticed. There are a few ways that you can handle the issue of the gavel vac not leading to a huge water change. 

1. You can vac a portion of the tank at a time with each water change, so like 1/3 at a time in a rotation. 
2. You can get a smaller siphon/vac which will take out less water while you are doing the change. I use a fairly small vac on my 10 gallon. I can vac all of the gravel before I have removed 15% of the water. 
3. With plants you probably don't want to disturb the roots so I would just do a light vac over those areas. Someone with more experience with plants can probably give a great explanation of this issue.


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## jones57742 (Sep 8, 2007)

Knight~Ryder said:


> Q: It's a commonly heard, but not completely accurate story, that water changes are bad and will kill your aquarium fish. How did the story start, and is there any truth in it?


KR:

No truth with regular maintenance but the story comes from the significant instantaneous change in water parameters produced by a massive water change in an unmaintained tank which produces stress for the fish.




dm800 said:


> But for people that have a bunch of plants in the tank, how do they vacuum the bottom with all those plants? Do they just skim the top of the gravel around them? Doesn't all the gunk build up under the gravel eventually?


dm:

If you have that much mulm on the surface of the substrate something is wrong somewhere*.

I now very, very rarely vacuum, like once every six months maybe, and almost all of the matter which I remove is snail shells.

When I do vacuum I do not attempt to get close to the base of the plants as there is really nothing there to vacuum anyway.

*In a fairly heavily planted tank which has plenty biological and mechanical filtration and which is well maintained with appropriate feeding no mulm should exist. 

Fecal matter will either be used by the plants' roots or decay and the ultimate nitrates produced therefrom will either be used by the plants' leaves for chlorophyll production or removed via WC's.

TR


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## dm800 (Nov 3, 2007)

I did try a smaller vac and can do the whole bottom while only taking out about 2-3 gallons. But then I went back to using the larger vac because I thought it was doing a better job because I could really see the stuff coming out. But if it is ok to use the small vac and not get as much stuff out, then I might go back to that way.


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## dm800 (Nov 3, 2007)

Jones:

There is no mulm visible to me on the surface of the substrate. I just thought I was getting it cleaner by pushing the vac way down into the substrate (almost all the way to the bottom of the tank) and seeing it come out. I just assumed it was fecal matter and it had to come out, but now it looks like I am overdoing it. So maybe I will just start skimming the smaller vac across the surface of the substrate. That sounds good to me because I was going to get more plants and thought it would be a problem to do water changes. So when you say you don't vacuum, do you just syphon out water without going down to the gravel to do your water changes?


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## Plecostomus (Jul 31, 2006)

lol Jones that is so true, people start complaining about how their fish die off after a big water change and it is just because the change is so fast that it shocks the fish. Oh and dm800, I recently learned from personal experience not to vaccum near the plants roots because the plants like having the mulm around their roots. If there is no mulm, the plant really doesn't have any dirt to grow in, because it can't take nutrients out of the gravel.


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## Plecostomus (Jul 31, 2006)

woah, you posted at the exact same time as me. You can push the vaccun all the way down to the bottom just as long as you aren't doing it near the plant's roots.


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## jones57742 (Sep 8, 2007)

dm800 said:


> So when you say you don't vacuum, do you just syphon out water without going down to the gravel to do your water changes?


dm:

In a round about way that is exactly what I do: I just siphon water out the top of the 110G tank and into two 5G tanks from which the water has been evacuated into the kitchen sink or house plant pots.

This is done daily and generates an approximate 10% WC for my main tank and 90% WC for the two 5G tanks. (Please note that these massive WC's in the 5G tanks do not produce the stress which I referenced in my previous post due to the daily WC's and the water temperatures being virtually identical.)

Where I was "whining" previously is that if you are getting a ton of deleterious material when you are vacuuming something is just flat not right out there.

TR


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