Cotton mouth

Question
I have a bala shark that got what we thought was cotton mouth last night, but this a.m. he was dead.  I have an South Asia (I think) black knife fish. Was told at the pet store if we treated the tank with anything the knife had to come out.  My questions A)what do i treat the tank with? B)does the knife have to come out? if so for how long? C) how do I treat him?
Thanks!

Answer
Hi Kim;

What are the symptoms of the sick fish? Are there any sick fish in there now? If there are no signs of illness in your other fish you shouldn't treat them at all. Even though medicines can save lives, they also have risks and most aren't useful to prevent infections anyway. Using medicines when not needed can cause organisms to become immune to them so they don't work when you need it to save lives.

Sometimes what we think is illness or disease is actually as simple as a problem with water chemistry or "New Tank Syndrome". If you do see a problem in your other fish, make a 25% water change before you use any medicine and have the water tested to be sure it's okay. Medicine can make water quality problems worse and the fish will be further stressed and could die as a result. Your local fish store should be able to do that for you. Have them test for ammonia (NH3) and nitrite(NO2). If either are above "zero" keep making partial 25% water changes daily until they are both under control.

Diseases attack fish if they are weak or injured. Keeping your fishes' immune systems strong will help avoid infections and illnesses. To do that, keep the water very clean, don't overcrowd, and give your fish a healthy diet. Change 25% of the tank water weekly and vacuum the gravel every couple of weeks, or even weekly if you have an overcrowding problem or tend to overfeed your fish.

Followups welcome....

At Your Service;
Chris Robbins