# Why does STAGNANT water kill fish?



## fish_lover0591 (Nov 11, 2006)

uhhh bettas can live in stagnant water but thats only because the breathe air from the surface. I think stagnant is way different then black water though. Black water is caused by dying leaves and organisms in the water. Stagnant means that the water isn't moving but you can create a tank where theres no water movement and you don't do water changes but you have lots of plants and top off your tank when water evaporates. Plus you didn't do anything to the water right ? its basically clean and free of bacteria and you did remove the chlorine and chloramine right? I would still start with new water lol .


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## crazie.eddie (May 31, 2004)

I've always thought of stagnant water as a small body of water with *no* circulation of any kind, basically still water. No current or agitation, no oxygen. No oxygen, fish die. When you age water, you are supposed to use water pumps or powerheads to keep the water moving.


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## Storm_Rider (Sep 30, 2006)

hmmm hmmm hmmm. well now i know. but yes, the water has been sitting perfectly still. clean as when it left the faucet. but i guess i'll drain it and refill it... 50 gallons.. uggh. i need to get a python or something. thanks for the help


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## BlueRam (Sep 21, 2004)

Storm_Rider said:


> hmmm hmmm hmmm. well now i know. but yes, the water has been sitting perfectly still. clean as when it left the faucet. but i guess i'll drain it and refill it... 50 gallons.. uggh. i need to get a python or something. thanks for the help


You can always try the smell test. If it smells like swamp you need to do large WC and circulate.


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## Solstice (Jan 9, 2006)

Gouramis are also able to live in stagnant water because they're labryinth fishes that have a special lung-like organ that allows them to breathe at the surface. Like others have said, one major contributing factor is the lack of agitation and inflow of oxygen that kill the fish.


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## Hypancistrus (Oct 28, 2004)

Storm_Rider said:


> So.. I've read in a lot of posts in various forums, including here, that stagnant water will kill fish.. but I've yet to see an explanation to why that is.


Stagnant water has little to no dissolved oxygen.

Fish do not breath water. They breath oxygen which is dissolved in the water. If the water has little to no dissolved oxygen, they suffocate.


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## Wasserpest (Jun 12, 2003)

Another problem with tropical fish kept in temperate climates in stagnant (or insufficiently circulating) water is that cold water is heavier than warm water, and collects on the bottom. The temp differences can be substantial, more so in taller tanks.


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## Storm_Rider (Sep 30, 2006)

Thanks for all the different answers! Someone told me yesterday that stagnant water has no bacterial change. i'm guessing that would lead to a buildup of ammonia and give me that smell BlueRam mentioned.


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## Hypancistrus (Oct 28, 2004)

There's plenty of bacteria in stagnant water, but it's what's called anaerobic bacteria. "Anaerobic" means not using oxygen, and that's actually a misnomer. Anaerobic bacteria does need oxygen. But it has the ability to take oxygen from nitrate (NO3) and sulfate (SO4). Nitrate reduction isn't a problem, as the only by product is nitrogen gas. But sulfate reduction produces hydrogen sulfide (H2S), which smells like rotten eggs and can be toxic to fish at high enough levels.


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