I don't want to speak to soon, but, a scrape of the heater this morning showed zero tetrahymena, and a tiny number of Costia in the Ranchu tub. All of which looked like they were about to die (going nowhere and spinning slowly on the spot). I think the increased temperature certainly played a huge role in the effectiveness of the FMG this time round. The Ranchu were being kept in water around 22 degrees C and the same during the last course. For this treatment course, I gradually increased the temperature which touched 26/27 degrees C during the final dosing. This no doubt helped speed up the life cycle of the parasites, meaning the chemical could go to work on a maximum number of Costia, in their free swimming form.
The Ranchu may be moved back into the main pond this evening, although the higher temps have been more manageable in the smaller quarantine tubs. I also want to avoid pulling them out of the final treatment dose too soon, like last time. For that reason, I have a large water tank (disinfected) that has been pre-dosed identically to the pond they are in. This will give me the opportunity to keep the ranchu in the treated water, that is also fresh, for a couple of days longer.
I have noticed a couple of the ranchu no longer gulp at the surface after feeding which is interesting. As it only seemed to occur after feeding, and by the largest, heaviest feeders, this was a symptom that could well have been put down to a number of causes. Clearing gills of debris, Begging for food, Poor water quality(not so likely), or gill damage. Although scrapes were taken for the edge of the gill plate, no scrapes were taken from inside the gill, making it impossible to know for sure, just what took up residence there. Having previously identified and treated for gill flukes and now costia, it's certainly not a stretch to imagine the gills may have been infested at some point. It now seems clear to me that gill damage/weakness was the issue, with the change in behavior observed.