HELP! Koi has mouth rot. HELP!

[Johnhale]

I am hoping someone can help. When feeding the fish today I noticed that one of the kois was eating strangely, then when it turned I saw that on one side of its face was deformed (I hadn't noticed this before today). I researched the symptoms it was showing and it looks a lot like mouth rot.
I am currently doing a water change in the pond, so can't measure the water levels, but I will describe the pond. It is 16x12x4 feet (4784 gallons), using a PondXpert SpinClean 20000 filter, as well as having a waterfall running from a small pond filled with watercress. The main pond itself has lots of oxygenating plants, there are around 8 koi, 10 gold fish, 3 or 4 rudd, a shoal of minnows, and a few stickleback.
I haven't been able to catch the ill koi yet, but want to know if mouth rot is contagious? What is the best method to rid the pond of parasites? Any advice/help would be greatly appreciated, thank you in advance.

 

[Johnhale]

Just updating to say that sadly the koi had to be euthanised this morning as the mouth rot had gotten into its bone. However, all of the other fish are perfectly healthy. I can only assume that the infection was caused by the algae bloom from all this sun we have had, as well as slight overfeeding.

 

[j.w]

@Johnhale Sorry to hear about your koi.
Hoping all your other fish stay well.

 

[Jhn]

Sorry about your koi. You should test your water to see what is going on. An algae bloom won’t cause your fish to get sick. Algae blooms are in response to excess nutrients in the pond.

 

[Mmathis]

Hello and welcome. Sorry to hear about your fish! Infection into the bone! Bummer, but glad that you recognized his pain and decided to euthanize him.

Agree that you should test your water parameters. I’ve never heard of an algae bloom causing illness, but if your water quality has any issues, that could for sure set the fish up for problems.