White spots/lumps on goldfish

[Terry's Fish]

I have about 15 goldfish in a 3400 Ltr tank (2.4Mtrs x 2.4 x .6) with filtration and UV and good aeration. It has been going perfectly since i started it over 3 years ago. Water is crystal clear and fish are lively. I feed them a little almost every day.

About 3 weeks ago i had to shut down the system for unrelated (electrical work) reasons. During this time the weather went from an unseasonable warm spell into more typical cold and frosty mode. After i got the pump/filter going again I noticed that one fish has a handful of white raised spots. I had not closely observed the pond for a few weeks prior so i don't really know how long the condition has existed. I obviously need to find out what the spots are before i can apply any effective treatment.
The only other possibly related factor i can think of is that i recently topped up the level with rainwater (which it has always been) but i noticed at the time that the rain water looked a bit dirty, probably from being stirred up by run-off from recent storms entering the tank. Could it be contaminated, i ask myself?

I am new to forums but will attempt to upload a photo that may help identify the disease. I've done the usual web searches for clues but it seems like so many diseases involve white spots! My guess is maybe Carp pox or Lymphocystis (the spots/lumps seem to be hard rather than fuzzy/wooly) but i really have no idea. The fish is still lively and behaves and feeds normally with the others.

My internet searches suggest that there is no cure for carp pox, so not sure what to do. Should i perhaps treat the pond with something like Pimafix (expensive but...) in case the problem is fungal or bacterial?

Sorry image is fuzzy, - they just will not keep still!

 

[ShawnInfirmity]

It's really difficult to see but are the lumps kind of wax-like to the touch? Meaning, do they have a malleable texture to them? It could very well be carp/fish pox but again it's hard to tell in the blurry photos. You might need to net the fish or handle it to get a better picture or to feel the lumps to see what kind of texture they have to them. AND of course, as with any suspected fish illness I would test my water parameters pH, ammonia, nitrites, and nitrates just to be sure nothing is "off" with the water quality.