For two days my fish has had a strange whitish spot on his left side and right side fin. Looking today, I noticed he had it now massively on his right side and the eight side fin looks as if it's only bones left.

As none of the other two (1 old male and 1 young female) has it, I am not sure if it's a fungus or if he had a fight with the other male. What's more is, he is breathing rapidly and looks like he is suffering from pain.

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Water parameters (measured with Tetra 6 in 1):

  • NO3- is 250+ ppm
  • NO2- is 1 ppm
  • GH is 8
  • KH is 3
  • pH is 6,8
  • Cl2 is 0 ppm
  • what does your water test say ammonia-nitrite-ph,what type of filter and heating do you have in your tank,was your tank properly cycled before you put the fish in your tank.here is some information on how to cycle a tank fishlore.com/NitrogenCycle.htm Commented Jan 4, 2020 at 12:35
  • Fish was originally from a different aquarium. Is in this one since half a year already (as is the other male. The female is here since 2 yesrs). In tank filter with the pads having veen changed 2 weeks ago. Water test yesterday looked ok heat itself is also in the norm. The other fish inside look good even 4 day old guppies (were just born) @trond
    – Thomas
    Commented Jan 4, 2020 at 12:41
  • what type of water test do you use and please post the readings of your water test ammonia-nitrite-ph please edit your question with the information. Commented Jan 4, 2020 at 13:24
  • @trond updated. The no3 qas higher today a lot. Maybe i did touch it accidently esterday
    – Thomas
    Commented Jan 4, 2020 at 16:21
  • It may be the same disease that wiped out my catfish and regular fish. I recommend getting medicine for it and treating it fast. Commented Jan 8, 2021 at 9:36

1 Answer 1


You need to stop feeding your fish for some time while you wait for the bacteria to grow to a level where they can handle the ammonia and nitrite in your tank.

To lower the danger of nitrite poisoning you can add aquarium salt so the concentration is at 0,3% salt in your tank (most fish will handle this concentration of salt for a long time).

You need to change about 20% of the water today to get the level of toxins down (remember to use a dechlorinator when you change water).

Take daily water tests until the level of nitrite starts to go down. In a tank that is properly cycled, this does not take long.

Next time you clean your filter be sure not to change more than 30-50% of the filter media to keep the biological cyclus going in your tank. You do not need to clean the filter until you can see the water flow is reduced.

If you have filter foam/sponges in your filter, you only need to rinse it. Be sure to use water from your tank when you rinse the foam to avoid chlorine killing the bacteria.

Your fish looks like it has got an fungal infection. If possible, treat your fish in a separate tank. This is to avoid medicating the main tank, as this will kill the nitrifying bacteria and cause problems for the rest of your fish.

  • Can it be that its not the bacteria for the ni3? Since a few bigger loaches got into the tank a few weeks back i lost a lot of the plants inside (ripped out of the soil/destroyed). Tried to get the parts but quite possible that a lot of parts were still there and total plants remaining are about 1/4th of what i originally had. Found no way so far to make any new ones resistant to the loaches(aka suffered the same fate)
    – Thomas
    Commented Jan 5, 2020 at 10:19
  • NO3 is nitrate it is normaly not dangerous but you have a lot of it so you need to change a lot of water,NO2 is nitrite and is toxic to fish and plants.when your fish uprooted the plants it might have released sulphur dioxide it is very toxic to all life,but this do only happen if you have not vacumed the gravel to remove rotting material in the gravel.you can fasten the plants on rocks and roots by using rubberband. Commented Jan 5, 2020 at 12:30
  • tnx did a water exhange just after your answer was posted yesterday (so hopefully the no3 is down). the anti fungal medicamentation is also not so good with just 4 days old guppies inside am I correct there? (fear then I will have to wait 2 days until shops are open again here to get a separate tank)
    – Thomas
    Commented Jan 5, 2020 at 13:46
  • it is definitly best to get a new tank but you can use water from the old tank so the temparature and PH is unchanged from what your fish is used to. Commented Jan 5, 2020 at 14:15

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