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Old 01-05-2017, 09:25 PM   #1
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URGENT: Should I return this aggressive fish?? Help Please!

So, I bought 3 Zebra Danios nearly a week ago to cycle in a 20 gallon tank. This is my first experience keeping fish.

I have done a lot of research, obsessively checked water levels (still 0 ammonia..) and done a single 10% water change (no need to do more w/o change in ammonia). I am confident I am doing the cycle the right way.

One of the three Zebra Danios is much larger than the other two. It constantly chases and nips at them. It seems to have gotten progressively worse the last day or two. Tonight, it wouldn't allow the others to eat, and would nip at them every time they came to the middle or top of the tank (the natural tank space they occupy). The other two Danios have been lurking around the bottom of the tank while the big one swims around the rest of it. This doesn't seem like normal Danio schooling behavior from what I have read.

I know Danios can be aggressive when sorting out social order in a new tank, and when they don't have a full school (also if water levels are off, but they aren't), so I was giving this some time, but the degree to which the aggression is occurring tonight is making me wonder if I should just return this fish, and get 3 new ones at my LFS. I was planning to add 2-3 more anyways, so returning the other would mean I could just buy an extra new one.

Do you guys think I should do this? Is this concerning behavior?

I am hoping to do this tomorrow or Saturday so I appreciate the feedback!
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Old 01-05-2017, 09:55 PM   #2
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Definitely return the fish, Its not going to get any better. I had similar problems with gouramis. I tried putting the aggressive fish in a fish net for a couple of days to help them adjust to one another but when I released the fish it went back to to chasing and attacking other fish. I also read if you rearrange the tank that might help, but it didn't for me. Good luck.
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Old 01-06-2017, 03:10 AM   #3
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Help! Should I return aggressive fish?

So, I bought 3 Zebra Danios nearly a week ago to cycle in a 20 gallon tank. This is my first experience keeping fish.

I have done a lot of research, obsessively checked water levels (still 0 ammonia..) and done a single 10% water change (no need to do more w/o change in ammonia). I am confident I am doing the cycle the right way.

One of the three Zebra Danios is much larger than the other two. It constantly chases and nips at them. It seems to have gotten progressively worse the last day or two. Tonight, it wouldn't allow the others to eat, and would nip at them every time they came to the middle or top of the tank (the natural tank space they occupy). The other two Danios have been lurking around the bottom of the tank while the big one swims around the rest of it. This doesn't seem like normal Danio schooling behavior from what I have read.

I know Danios can be aggressive when sorting out social order in a new tank, and when they don't have a full school (also if water levels are off, but they aren't), so I was giving this some time, but the degree to which the aggression is occurring tonight is making me wonder if I should just return this fish, and get 3 new ones at my LFS. I was planning to add 2-3 more anyways, so returning the other would mean I could just buy an extra new one.

Do you guys think I should do this? Is this concerning behavior?

I am hoping to do this tomorrow or Saturday so I appreciate the feedback!
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Old 01-06-2017, 09:04 AM   #4
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Originally Posted by Spaullba View Post
So, I bought 3 Zebra Danios nearly a week ago to cycle in a 20 gallon tank. This is my first experience keeping fish.



I have done a lot of research, obsessively checked water levels (still 0 ammonia..) and done a single 10% water change (no need to do more w/o change in ammonia). I am confident I am doing the cycle the right way.



One of the three Zebra Danios is much larger than the other two. It constantly chases and nips at them. It seems to have gotten progressively worse the last day or two. Tonight, it wouldn't allow the others to eat, and would nip at them every time they came to the middle or top of the tank (the natural tank space they occupy). The other two Danios have been lurking around the bottom of the tank while the big one swims around the rest of it. This doesn't seem like normal Danio schooling behavior from what I have read.



I know Danios can be aggressive when sorting out social order in a new tank, and when they don't have a full school (also if water levels are off, but they aren't), so I was giving this some time, but the degree to which the aggression is occurring tonight is making me wonder if I should just return this fish, and get 3 new ones at my LFS. I was planning to add 2-3 more anyways, so returning the other would mean I could just buy an extra new one.



Do you guys think I should do this? Is this concerning behavior?



I am hoping to do this tomorrow or Saturday so I appreciate the feedback!


There are large types of zebra danios and small types, you may have accidentally gotten a big type, which tend to be aggressive. I also think that the fact of not having a full school could be affecting it. That way, they can work out a much more equal social order. Good luck!
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Old 01-06-2017, 09:48 AM   #5
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There are large types of zebra danios and small types, you may have accidentally gotten a big type, which tend to be aggressive. I also think that the fact of not having a full school could be affecting it. That way, they can work out a much more equal social order. Good luck!
+1
My girlfriend had the same problem when she got her fish from Petco

You just need more of them. It's always better to start out with at least 5. I then usually add them 3 at a time to upgrade my schools.
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Old 01-06-2017, 09:51 AM   #6
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yeah you can try tank dividing temporarily, rearranging the decoartions, or even putting him in new tank and then readding him (sometimes mine have been less aggressive as the "newbie" to the tank) but ultimately you can't not do anything so taking him back might be the simplest and surest option
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Old 01-06-2017, 11:29 AM   #7
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Spa...

A few things I see. No plants? You need floating plants in there. Water lettuce, Water sprite, Hornwort, Anacharis maybe. Plants calm the fish. They filter the water, are a food source and allow the bullied fish to hide.

Not enough fish in the tank to cycle it. 3 to 4 for every 10 gallons of water. Otherwise, all the water dilutes the fish waste to a level where the bacteria colony can't grow. Danios are good choice, just get a few more.

Testing strips are really the way to go. They're reliable as long as the package hasn't expired. Get the fish in the tank and feed a little every day and test the water daily for traces of ammonia and nitrite. If you have a positive test, remove 5 gallons and replace it with tap water treated with a dechlorinator. Just feed a little, test and remove and replace the water when needed. When several daily tests show no traces of ammonia or nitrite, the tank is cycled. Then, you just remove and replace half the water every few days to maintain safe water conditions.

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Old 01-06-2017, 03:29 PM   #8
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Thank you everyone.

Yes, there are plants (not live) in there and some places to hide.

I plan to return the larger Danio and get 3 more smaller ones. This will bring the school to 5 fish and hopefully lead my tank to begin cycling, and more peace among the fish.

Thanks.
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Old 01-06-2017, 05:15 PM   #9
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Originally Posted by Spaullba View Post
Thank you everyone.

Yes, there are plants (not live) in there and some places to hide.

I plan to return the larger Danio and get 3 more smaller ones. This will bring the school to 5 fish and hopefully lead my tank to begin cycling, and more peace among the fish.

Thanks.


It's not a school if it's under six. The rule is three to four for every ten gallons when it comes to fish in cycling. Good luck!
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Old 01-06-2017, 05:32 PM   #10
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Quote:
Originally Posted by BBradbury View Post
Spa...

A few things I see. No plants? You need floating plants in there. Water lettuce, Water sprite, Hornwort, Anacharis maybe. Plants calm the fish. They filter the water, are a food source and allow the bullied fish to hide.

Not enough fish in the tank to cycle it. 3 to 4 for every 10 gallons of water. Otherwise, all the water dilutes the fish waste to a level where the bacteria colony can't grow. Danios are good choice, just get a few more.

Testing strips are really the way to go. They're reliable as long as the package hasn't expired. Get the fish in the tank and feed a little every day and test the water daily for traces of ammonia and nitrite. If you have a positive test, remove 5 gallons and replace it with tap water treated with a dechlorinator. Just feed a little, test and remove and replace the water when needed. When several daily tests show no traces of ammonia or nitrite, the tank is cycled. Then, you just remove and replace half the water every few days to maintain safe water conditions.

B

I'm going to suggest care is taken with selecting testing strips to use. The ones I have used for the pool come in a sealed foil and still have issues under-reading. The ones I have used for the tank also under-read and don't have ammonia.

Perhaps it is something to do with our hot summers but ime I'm sticking with solution/vial test kits.
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