Help Please with a Strange Unknown Growth Around One Koi Mouth For Identification - has anyone seen this before ?
Habitat is a 700 gallon pond containing 10 koi with body length 10 to 14 inches.
Filtration turning over the water approx. every 1.5 hrs is firstly through a sealed pressure filter passing output through ultra violet light unit & magnetic unit to a second separate two chamber filter with different sized filtration sponges , firstly ‘ large ‘ then ‘fine ‘ perforations . The pond is stocked with plants which the koi have grown up with & do not damage . The filters run continuously as do 5 air stones . Maintenance is rotating renewing sponges with new as required less in the winter & more in the summer . Some filter sponges have been changed a month ago & different ones changed a few days ago , allowing for residual filter sponges with bacteria . There must be a lot of resident bacteria in this fairly thickly planted pond.
The pond as now has been running for a least 15 years with the last new fish several years ago , minimum 4 years ago & no new plants added in the same timeframe .
Temperature is seasonal ranging progressively from freezing to approx. 30 degrees .