Simply Koi and More Koi

All koi are feeding well, however 1 or two are showing signs of problems by sitting on the bottom between feeding, not all the time but some of the time and has progressivly got worse over a few days. Time to lift the koi and do a scrape,I have spent all morning doing scrapes I also scraped several other koi which apear normal.Checked at both 100 & 400 magnification, absolutelyl nothing.I was really hoping to find somthing I could treat. However I did notice on about 3 of the koi, there was a obvious lack of mucus, an almost dry feel. Surely this is caused by overproduction of cells and eventually dried out due to parasites? If so which ones and what is the best approach.
All parameters are normal p.H 7.3 Amm/Nitrite/nitrate all reading zero TDS 80. Nothing has been used in the way of treatments since last year. I would be gratefull for any help.I am starting to think down the lines of treating for costia as perhpas I might of missed when using the microscope
Best Regards Dave

Hi I would start at 100 then two three then four hundred.you may have missed something jumping from 1 to 4.Just a thought

Dave
What temp are you at? And have you had some temp flucuations over the weekend? Or a lot of rain water entry?
Tom

tomc wrote:Dave
What temp are you at? And have you had some temp flucuations over the weekend? Or a lot of rain water entry?
Tom

15 deg Trying to maintain this but fluctuating about 1 deg answer is no to the last one
Regards Dave