Fungus i think

Question
tank is over a year. 66 gallons. i live in the tropics Trinidad to be exact. i have three 3'' irridescent sharks and 5 half inch parrot fish in the tank at present. about six months ago a very rapid fungus spread through the tank killing the two kois and two gold fish i also had in the tank. when i say rapid i mean one sunday evening i noticed a white film or second skin forming on the koi but couldnt get to store as it was closed the next morning all koi and goldfish were dead. i emptied tank and refilled. putting back the irridescents and parrots which seemed unaffected. about a month later i added two young koi. the very next day they had the film again. I treated with pimafix and melafix which seemed to work. i was changing water regularly but the fungus kept coming back. they eventually died. irridescent and parrots unaffected. what should i do. is it at at all possible to get rid of fungus without having to remove gravel from tank. someone told me to bleach tank and refill using chlorine remover when filling and someone else said to use salt water to kill fungus. how should i clean the filter also. it is an eheim 2215 canister filter. i hope u can help.

Answer
Hi Paul;

I don't think you have to do anything at all except avoid coldwater species of fish. If you ran bleach through the whole system it would kill all the beneficial bacteria that keeps the water clear and keeps waste toxins low. It isn't necessary in your case and wouldn't be helpful anyway. If it were a contagious disease the parrots and irridescents would be sick too. Those fish are tropical and can tolerate the higher temperatures. Even if koi and goldfish seem okay at first, they eventually succumb to the stresses of the heat. They require temperatures below 72f to stay healthy on a long term basis.

Eheim is an excellent filter! To clean your eheim, simply rinse out the sponges and any other media. You want to rinse them in water that is close to the temperature of your tank water so the beneficial bacteria is preserved. Don't ever replace any of the pads or filtering media unless it is literally falling apart or you can get enough of the crud out to make it flow again. Replacing them causes the system to lose it's bacteria  which can be deadly to your fish. Toxins build up because bacteria is no longer there to filter them out. It will take 6 weeks for it to become "mature" again. Of course, the manufacturers and stores will say to replace them every so often. That's how they make money on you as a repeat customer! Don't fall for it. Just rinse and go. ;-)

Before plugging the filter back in to electricity once you rinse the media, fill the canister with water. Seal it up and it should start on it's own.

At Your Service;
Chris Robbins