Simply Koi and More Koi

just noticed this on my sanke:

we had a lot of this last year, i don't think anyone got to the bottom of it then, but i don't think any of it amounted to much as in no deaths or ulcers developing from it it was just benign mucus i think

Ahh, I remember a similar thing on my other sanke a couple of years back now I think of it. I scrapped a few fish and found a few of the usual suspects, not enough to cause concern, but seeing as I had some fmg that was coming close to its sell my date I added a 250mil bottle of nt labs FMG enough for 9000l into my 7500l pond and once the blue had faded, no more dodgy looking mucas. On both occasions the effect was in the same place just below the shoulder on the head skin.