While parasites of various types are often responsible for fish rubbing themselves against objects in the tank, sometimes to the point of causing raw skin, it can be difficult to identify which parasite it is, unless you have a very good visual of it.
In the case of skin fluke, which is a parasitic flatworm, they are unlikely to show themselves to the extent where you would be able to remove them manually as you can with leeches or fish lice. One of the common denominators they have with other parasite infections, is they can cause redness of skin, but so can rubbing against stones and wood. However, skin fluke also causes a fading of color, and because the treatment is common to other types of parasites, you are best to go with a general medication, such as Droncit or formalin baths, when unsure whether it is skin fluke or not. Remove severely affected fish to a hospital tank.
The standard treatments of adding 1 tbs. of aquarium salt to a daily change of water in the home aquarium, and raising the tank temperature by four degrees also applies. This is used for most parasites, including gill fluke, which has more obvious and visual symptoms.
Gill fluke is a worm that specifically attacks the gill membranes, causing them to turn red and acquire a coating of slime that makes it difficult to breathe. Fish will hang at the water's surface, gasp, and lose weight rapidly. The same tank treatments as skin fluke can be used, but with gill fluke, removing to a hospital tank and adding short baths in either formalin, salt or ammonium hydroxide to the regimen will help kill what is on the fish, and you can then treat their environment.
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