deep hole on tail of clown knife

[psychosicc6six6]

my 9in clown knife has a white hole on him it looks as though it is getting deeper
when i first noticed the dime size spot it was just a white discoloration, no hole, the spot isn't getting bigger in diameter only deeper. like something is eating a hole through his tail there are no other spots on him like that, and all of my other fish are fine, no holes or dime size white spots
any suggestions?

in my gallery is a pic of the hole...not a very good one though

the hole is pretty deep still the diameter of a dime but as deep as a nickle if not deeper

 

[guppy]

It looks like the kind of ulcer caused by heteroplaria, if it is it will respond to metrodazole baths, it will also probably respond to daily swabbing of the ulcer with either iodine solution or hydrogen peroxide but that is pretty stressful on the fish. One method to minimize risks to both yourself and the knife is wear surgical gloves to preventany more disturbance to the slime coat and introduction into nicks in your skin, and use a black plastic bag to catch and hold the fish instead of using a net. nets tend to abrade the fish.

 

[psychosicc6six6]

Thank you for you response.
But before I try the iodine solution (i have betadine, is that ok to use?) I'd much rather try something that doesn't involve catching & handeling the fish.

Would something like Melafix or Pimafix work?
And if so, can i just add it to the tank instead of moving my knife to a quarentine tank?

I have 2 Brown Knifes, a Black Ghost Knife, Dinosaur Eel, *Ornatipinus Eel, Peacock Eel, Yellow Cichlid, 2 Needle Fish, 2 Angel Fish, a Rope Fish, Synodontis eupterus, and 2 Clown Knifes, one about 4 inches & one about 9 inches, which is the one with the hole in him
Should any of those fish no be exposed the Melafix or Pimafix.

 

[guppy]

I have no personal experience with the mix but have read that cory cats tolerate it and even baby whale mormydids so it should be okay with knives and those are the most sensitive to meds of the fish you have listed.