sounds like you overdosed the pimafix.
To work out the volume of water:
measure length x width x height in cm.
divide by 1000
= volume in litres.
When you measure the height, measure from the top of the substrate to the top of the water level.
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Do a 25% water change and gravel clean the tank to dilute the pimafix and see if it helps.
Make sure you don't have any carbon in the filter if treating with medications because it will absorb medications.
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What other fish do you have in the tank?
If you don't have discus, wild angelfish or wild catfish, you can add salt to the tank for the protozoan/ fungal infection. Fungus is white fluffy stuff that stands upright from the body. Protozoan infection looks like a white patch but does not have fluffy bits sticking up.
Use 1 heaped tablespoon of rock salt, swimming pool salt or sea salt for every 20 litres of tank water. If there is no improvement after 48 hours you can add another heaped tablespoon of salt per 20 litres.
If you can post a picture of the sick fish with the white stuff we should be able to give you a more accurate diagnosis.
