i had an infestation once with a protazoa like that .
under the microscope i could see them once in a while burst open and swarmer calls would be expelled .
i treated it with metronidasol in the water and food .
fortunately they were still eating some food , you can try soaking cubes of freeze dried australian black worms .
they might take that , in combination with long term baths .
i achieved complete cure and have not seen anything in a year .