Why Did Old Platys Die When Adding New Ones

SirGeoffery

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Hey all,

I thought it was time to get some extra fish.

I have a 90L(24Gallon) with plants. Current fish at the time of adding were 5 platys, 6 bloodfin tetra and 5 corys. I got 4 more platys, two micky mouse ones and two yellow/black ones (not sure what they are called). Got them from the same place I got all the other fish.

After about a week, my existing 5 other platys had died, the only symptoms were one was hanging out near the top sort of almost trying to eat the top of the water, but none of the other platys did this, and the corys and tetras are fine.

My water levels and temperature are fine, 0 nitrites, 7.5 ph (which is normal for my tank), nitrates 15-20ppm, kh and gh normal.

I can't work out what happened, the only sort of hunch is stress - the new fish seem quite aggressive at feeding time. They also seem to sit in the middle of the tank and all the other fish tend to move to the sides a bit, but not super obvious unless really watching.
 

Aubreew

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Hanging out near the top sort of almost trying to eat the top of the water
That kinda sounds like gasping for air. If no other fish are getting sick then you might be right about stress. Can you tell if you somehow got all males? That would certainly put stress on the chain of dominance that the other platy already had in place, however, usually if there is an issue with dominance the stressed ones won't go near the waters surface for food. So if they weren't somehow ill I really can't say what caused them to die. Hopefully someone with a little more platy experience will know.

If you figure out its a dominance thing and got all males, try getting 1-3 females per male (without overcrowding). That should help. By aggression at feeding do you mean they act like little piggies or that they fight? If they fight I think you need more females.
 

Rtessy

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Do you have any way to test for ammonia? It sounds a lot like ammonia poisoning. Also it sounds like you're using testing strips, they're often not at all reliable. I think it's definitely worth investing in the API freshwater master test kit. You can go to most stores and get it tested, but they'll just tell you "it's fine". You'll need to get the actual reading. Even though you have nitrates, the addition of these folks may have caused an ammonia spike
 

Aubreew

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I
Do you have any way to test for ammonia? It sounds a lot like ammonia poisoning. Also it sounds like you're using testing strips, they're often not at all reliable. I think it's definitely worth investing in the API freshwater master test kit. You can go to most stores and get it tested, but they'll just tell you "it's fine". You'll need to get the actual reading. Even though you have nitrates, the addition of these folks may have caused an ammonia spike
I didn't even think about ammonia poisoning! As it can damage the fish's gills (making the fish gasp for air at the top) that is very likely what happened.
 
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SirGeoffery

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Not using test strips, could be ammonia poisoning but why are all the other fish fine. If we assume one fish poisoned, any ideas about what happened to the other 4?

Thanks for feedback so far.
 

Fishie_Mom

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The other fish may have tolerated it better is all. Some fish are more sensitive than others are.

Adding new fish without quarantining also opens you up for spreading disease to all your old fish. So this is a possibility also. You may have brought some sort of infection into the tank.

More than likely this sounds like you overwhelmed your nitrogen cycle, and they died because of an increase in ammonia. I would recommend using Seachem Prime to detoxify the ammonia next time. Use it daily as a preventative, for 3-4 days after adding new fish. It will protect them from the mini-cycle caused by increasing your stock.

Also quarantining all new fish for 3-4 weeks prior to adding to your display tank, will also help keep a healthy tank.
 
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