Trying to do fish-in-cycle and one zebra danio is bullying the others

TheCount

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My wife wanted to buy an aquarium, and she didn't want to wait for a fishless cycle to complete, so we ended up getting a 29-gallon aquarium and we have been trying to do a fish-in-cycle. We started with 3 longfin zebra danios, and the store employee got me 2 fairly fat ones that we thought were females and 1 fairly skinny one that we thought was a male. But when we put them in the tank, the biggest one, which I thought was a female, often bullied the other 2 fish. I read that behavior like that could be from not having enough fish in the school, so a few days later we added 3 more zebra danios, but these were the regular breed (not the longfin), and they were smaller. But the bullying continued, and during the next 2 weeks, 2 of the regular zebra danios died, and I suspect that the bullying might have contributed to their death, because the other fish all seem quite healthy, and my water readings all seem fine (which is actually weird, because it is a new tank). I'm not sure what to do about the bullying danio.

The other issue that I am concerned about is that my aquarium doesn't seem to be progressing through the nitrogen cycle. I was expecting the ammonia to go up, and then the nitrites to go up, and then the nitrates. We have had fish in the aquarium for about 2 1/2 weeks, and I have tested the water every day, and every time the ammonia and nitrites were 0 or very low. I even took water samples to the local fish store, and their readings were the same. The readings are now showing small amounts of nitrates. Is it possible that the plants in my aquarium have been absorbing enough ammonia and nitrites to cause the tests to read so low? If so, is that slowing down the growth of beneficial bacteria? We have been making 20-25% water changes twice a week. Is that disrupting the growth of the beneficial bacteria? How can I be sure that my aquarium is progressing through the nitrogen cycle?
 
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mattgirl

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If this is a heavily planted tank it is very possible the plants are clearing out the small amount of ammonia so few fish are producing. First I would stop changing out so much water. If you knew me you would know that is not something I say very often. If you aren't seeing any ammonia or nitrites there is no need to be doing water changes twice a week.

Have you run the nitrate test on your source water? That could be where the nitrates you are seeing are coming from. Or... are you adding any ferts for your plants. That too could be where they are coming from.

The cycle needs ammonia to move forward. Since you are doing a fish in cycle you may need to consider adding more fish so there will be more ammonia than the plants can use.

Oh, and where are my manners. Welcome to Fishlore :)

Edited to add: You may want to consider returning the bully.
 
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TheCount

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Thank you for your response. The tank isn't heavily planted. It just has 2 java ferns, an anubias, 2 patches of java moss, 2 marimo moss balls, and a little bit of crystalwort. I'm not adding any fertilizer.

I took a water sample to my fish store today, and their test showed some ammonia. I think maybe my ammonia test strips aren't any good, because they are showing 0 ammonia.

I tested my tap water, and it is showing about the same amount of nitrate as my aquarium, so that must be the source of the nitrates.

I didn't even know that you can return fish to fish stores. The bully has settled down somewhat recently, and the remaining danios seem to be able to tolerate it okay. If the bully causes any more problems, I will try to return it. Thanks for that suggestion.
 

mattgirl

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I will suggest you get an API Master freshwater test kit. When doing a fish in cycle it is a good Idea to keep a very close eye on the parameters (pH, ammonia, nitrites and nitrates) and all the tests for them are in the test kit. In my humble opinion it is more reliable than any of the test strips.

Not all stores will take fish back but some will. If the bully doesn't settle down you may want to check to see if yours will.
 

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