Why do fish stay under filters?

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Reign

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Jul 7, 2012
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So I have 3 Zebra Danios in a 29 gallon that is cycling. They've been in there for a day and a half now, and I noticed that they seem to like staying under the filter for long periods of time. Yesterday, the smallest Danio spent around an hour or two just hanging out under the filter, then the second biggest decided to join it shortly after. Today, the biggest is staying under it right now and looks like it's going to spend the night under there. Is staying under the filter comfortable for them?

The filter is a Fluval C3 power filter, so the stream of water coming out is pretty strong and makes some bubbles, which they seem to like trying to eat, and I also have two airstones which makes the water move a bit.
 

JamieMonster

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Mar 16, 2012
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Well- putting a fish into an aquarium that is cycling is EXTREMELY stressful, and physically damaging for them. I would imagine it isn't too comfortable, and that the danios probably feel pretty sick. Under the filter would provide a place that seems to be sheltered and dark, which, in their stressed condition, probably provides at least a little comfort and security. Fish who are ill will also frequently seek out dark and secluded areas to hide when they aren't well. It just feels safer there, and is a natural defense mechanism for a fish who isn't well.
 

mesto

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Apr 28, 2012
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When you are cycling, it is a sign of stress. That is the most oxygen rich water in your tank. Both ammonia and nitrite that build up in a tank during the cycling process inhibit your fish's ability to breathe and process oxygen, basically. If you do not have one already, I'd get an API Freshwater Master test kit and test daily since you are doing a fish-in cycle. Any readings above 0.25 for ammonia or nitrite, do a water change with clean temp-matched dechlorinated water.

Later, fish hanging back there can do so because they like playing in the current. But in your case, since you are in a cycle, I would take it as a sign of stress and act accordingly. Good luck, keep us posted!
 

nerdyrcdriver

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My betta does that with his filter as well. Sometimes my guppy will do that too, but I think for him it is to stay out of the current.

Edit: But I do testing on my water, and both of those tanks are cycled.
 

Reign

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Jul 7, 2012
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Well, apart from the time it spends hanging by the filter, the Danios, especially the biggest one seem to really be active and swim all over the place, and they also seem to like bumping into the glass, but not very hard, I think they are chasing their reflections. They also ate food, I fed them one flake each today, but the biggest one snatched one of the ones meant for the other Danios.

There's also a fair number of decorations in the tank, with places they can enter, so if they wanted a dark place, one of those would probably be better. Also, they seemed to become more active when I turned on the aquarium lights earlier today, even the smallest one which seemed really shy and hid whenever I came went and played with the other two.


I do have the API liquid kit, but I had to wait around 24 hours since I had used Prime to dechlorinate the water, so I just recently tested ammonia, before doing a 3.5 gallon water change. The test came up zero(yellow), but because I'm sure the time Prime stops acting isn't set in stone, I kept a clean vial of the tank water before doing the water change, which I plan to test tomorrow when I am sure that Prime has stopped detoxing the Ammonia.


Also, mesto, you mentioned they like playing in the current, and I noticed that the fish all face to the right when hanging by the filter, they face against the current which is made because the air stone at the right side produces big bubbles that move a bit of water when they surface.


So I will test the clean vial of tank water tomorrow, and see if it is ammonia causing them stress. Thank you for helping.
 

mesto

There's a FISH in the percolator!
Apr 28, 2012
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Depending where you are in your cycle you may have no ammonia but high nitrIte levels. I would test for all 3- ammonia, nitrite, nitrate, do you can monitor the cycle and know when you are done with this cycle (doing fish-in, you will have a mini cycle every time you add more fish).

How long has the tank been set up? Have you monitored ammonia levels and seen them rise at any point yet?
 

Reign

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Jul 7, 2012
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Depending where you are in your cycle you may have no ammonia but high nitrIte levels. I would test for all 3- ammonia, nitrite, nitrate, do you can monitor the cycle and know when you are done with this cycle (doing fish-in, you will have a mini cycle every time you add more fish).

How long has the tank been set up? Have you monitored ammonia levels and seen them rise at any point yet?


Nope, it's only been up a week, mainly doing nothing, and the danios were put in around 2 days ago now, so I didn't test the nitrite. Haven't seen ammonia rise at all. The biggest one that I mentioned was spending the night behind the filter is now darting back and forth quickly at the top, near the filter, so I think she's fine.
 

bettalover77

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May 27, 2010
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It kindof sounds like your cycle hasn't started at-all, but that could be because of the prime. if it hasn't... I reccomend testing EVERY day (do that anyway)

good luck!

(is this your first tank?) if so congratulations!

regards
 
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