If you have catfish then put some plants or ornaments in for them to hide in. Alternatively, turn the tank light off so it's not as bright for the fish.
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The bristlenose is covered in whitespot.
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You need to get the water to 86F, if you have water movement in the tank from the filter, the entire tank should be the same temperature.
If you the heater won't go any higher, put a cover on the tank and insulate the back and sides of the tank with polystyrene foam or a towel or blanket. Make sure it can't get wet.
Close the windows and door to the room the tank is in and try to keep the room warmer so the heater doesn't have to work as hard.
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You do the gravel clean and water change each day to remove any whitespot parasites that have fallen off the fish. You do this for 5 days so you get rid of most of the parasites in the tank. This buys the fish a bit of time while the heat kills the parasites.
Normally if the whitespot had only just started, I would say do 1 big water change at the start, but because this has been going on for a couple of weeks, you need to do the daily water changes and gravel cleans for 5 days to compensate for the fact there are so many whitespot parasites on the fish and in the tank.
Each day more spots will fall off the fish and you will hopefully remove most of these when you do the gravel clean. This leaves fewer parasites to hatch out in the tank and potentially reinfect the fish.