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White splotches - fish died very quickly when I tried treating


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I am an inexperienced fishkeeper but have been doing well for the past 6 months largely in part to the resources provided by Aquarium CoOp. I have longfin serpae tetras in a community tank and I saw some white splotches on two of them, as well as a bit of fin rot. I'm assuming this happened due to fin nipping as they can be quite aggressive. They are larger splotches, not dots like ich, so I thought it could be columnaris or some kind of fungus. I've never treated sick fish before, so I got a sterilite bin from Walmart and rinsed it out, put a heater and a cycled sponge filter from my main tank in it, and filled it up with water with the same parameters as my main tank. I then dosed it with IchX and Maracyn according to Aquarium CoOp directions.

My fish appeared healthy in my main tank besides the splotches and their fins, but after I moved them to the hospital tank described above they died within an hour. This seems like a very quick time for them to go from swimming happily to completely dead, so I am quite confused and want to know what went wrong. Any thoughts? Thanks!

white splotch.jpg

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Sorry to hear.

Lots of things can go wrong in a Quarantine / hospital tank set up. Without doing a rigorous troubleshooting project, there's a lot of guesswork.

Possible things to check:

(1) Are you sure the temperature was in the safe zone?

(2) Are you sure that the sponge filter was seeded properly?

(3) Could the container have been coated with a harmful substance -- wiped down, etc?

(4) Did you use _tank water_ or _tap water_? -- If tap water, did you remember to dechlorinate it? If tap water, are you certain that the parameters are very close?

(5) Could you have overdosed the treatment?

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Thanks for your reply.

1) yes I matched the temp to the 76 it was in the tank

2) it has been running in my main tank for 5 months, and even so I don't think ammonia from one fish could kill it within an hour right?

3) I wiped it down with a paper towel and water but it's always possible I guess. Nothing has ever been in it except fish though.

4) I actually use remineralized RO water and I matched it to the GH, KH, and pH of my tank.

5) I used exactly 5g of water and added 2.5 mL IchX and 30 mg Maracyn as per Aquarium Co-Op ratios.


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Looking at the picture I would say your dealing with columnaris that a gram negative bacterial infections that spreads more quickly at temperature over 75 and can kill your fish in 24hr to 7 days for some of the cold water stains if other fish are showing symptoms then I would with a combination of kanaplex and jungal fungus clear fizz tabs containing nitrofurazone following this treatment plan @grape


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