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Freshwater Aquarium/Fish disappearance


I have just set up a new freshwater tropical aquarium. It is a 40L tank. I left it to cycle with some live plants in it for 2 weeks and 5 days before adding fish. I added 3 neon tetras 5 days ago. 2 days ago I added some aquarium salt as the guy in the shop said it was beneficial for gill health etc. I added the correct amount for the amount of water in the tank. I had noticed that one of the tetras seemed to be on his own a lot and the other 2 tended to go around together.

Last night I had 3 neon tetras. Tonight I have 2. I have lifted out the ornament to see if it is inside, moved and checked all the plants, even checked inside the filter. He didn't appear when I fed them and I can't find him anywhere at all.

I am baffled, I have kept fish before although not for nearly 10 years, but in my experience if a fish dies it floats and I would remove it, but there is no sign of this fish whatsoever.

So my question is several pronged. Firstly, I am guessing it has died, would the other 2 have eaten it since last night leaving no trace whatsoever?

Secondly, what might be the cause of it dying? Is it something I have not done correctly? Or was it likely to be ill given that it has been separate from the other 2 more often than not? I was going to go back this weekend to get another 3 little fish but am worried now.

Thanks for your help.

Hi Emma

It most likely died. Fish don't always float when they die, more often you find them laying on the bottom of the tank. The others could've eaten at it and maybe the remains moved around in the tank with the flow of the water and were taken into the filter or buried in the gravel somewhere.

Something was definitely wrong with him if he drifted off on his own. Neons are a schooling fish and stick together. Test your water or take a sample to your pet store and have them test it for you. If all is well, it is safe to add more fish. I wouldn't worry about the Neon that died, if the other 2 are fine, he was likely ill when you purchased him.

Hope this helps, good luck!  

Freshwater Aquarium

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Richard Hight


I own and maintain several freshwater aquariums from 2 to 180 gallon. I can answer most questions about freshwater aquariums, including setup, cycling, maintenance, compatible tank mates, feeding. Moving? I've moved fish both across town and across the country and can help you get your little aquatic friends to their new home safely. I know and have experience with most freshwater community fish, South American Cichlids and African Cichlids. I don't answer questions about Goldfish or keeping Goldfish with Tropical Fish. I also don't answer questions about keeping crustaceans (shrimp, snails, crabs etc) with Tropical Fish, nor questions about saltwater fish or aquariums. I'm not available to answer questions on weekends, this is when I do maintenance on my own tanks.


Many years of personal experience with community tank fish, semi-aggressive fish (Barbs, Tetras, etc), Angels, South American Cichlids and African Cichlids.

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