Platys Abruptly Dying


So, on Tuesday April 24, I purchased 6 Red Wag Platys and 3 Cory Cats for my 20 gallon aquarium.

Since then, 4 of the 6 Red Wags have died and the Corys are doing just fine. They're dying really suddenly- till Friday they were really happy and healthy with no signs of trouble. One of the males died Saturday- I thought it might just be one unhealthy on out of the bunch since his back fin was a little torn prior. Then today (Sunday), I came home from work with 3 more dead and the last two not looking great either.

I'm trying to figure out what's going on with them, Especially since this has happened really abruptly with no signs of sickness.

The tank is fully cycled and has been established for over a year, and has lots of plants (2 Anubias, 2 Four Leaf Clovers, Water Sprite, Ludwigia Peruensis, and a bunch Ludwigia Needle Leaf) and 2 Nerite Snails.

All water parameters are good;
Temperature at 78
pH has been steady at 7.6
Ammonia at 0
Nitrites at 0
Nitrates at 5-10 ppm

I called the store I purchased them at, to see if anything was up on their end- all good there.

If anyone could give me any information or help me find something I overlooked, I'd love to know. This has been super frustrating and sad. I just want to figure out what's going on before I replace or add to the tank again.

I'll be getting my water tested at a store within the next couple days so hopefully I can get some more numbers in the next few days.


You're overstocked, unfortunately. Some members will tell you not to put Platys in a 10 gallon at all, I would personally say 3 female Platies and that's it. No other fish. If there's too many males and not enough females, the females can get extremely stressed out by the males chasing them around trying to mate, with no place to escape. I know other members will also tell you that Cories need more than 10 gallons, and I agree, it's not enough space. I feel that the store messed up the test, because I'd be shocked if the bacteria was actually able to handle 9 fish being added at once without a spike in ammonia and nitrite. I'd also assume your nitrates wouldn't be that low. I'd advise you to order the API liquid test kit on Amazon for $19 usd, I wouldn't rely on others or the strip tests they probably used.
  • Thread Starter


Sorry, that should say 20 gallons, my bad for the typo.
The platy mix in the tank was 1 male and 5 females.
And the results were with the API liquid test kit; what I said was I am planning to go to a store to get a test done for more information.

As an update, all the platys have died. All that's left is the Cory Cats.
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