What to do with my tank after a fish dies

Question
I have a 30 gallon tank with 2 orandas that are about 3 inches a piece in it that has been set up for about a month. I have a Biowheel filter and the water condition is good - there is no ammonia or nitrate level problems and the pH is slightly acidic (like a 6 rather than a 7) and I have put Freshwater aquarium salt in the tank also to help with any stress there may be. I do about a 10% water change weekly. Lately one of my fish was acting intermittently sluggish and was floating at the top a lot so I fed both of them peas (which they loved) in case of a bladder problem and permanently turned off the light which used to be on for 4 hours a day just in case it was stressing him out. I did a larger water change and made sure the levels were fine. The next day, the floating fish had 3 white spots on his head so I treated the tank for parasites just in case. The next day I treated the tank for Ick (the 2 medicines said they could be used together within 24 hours). A day later (today) the spots were smaller (so it was probably not ick) but the fish was more listless so I did another water change and put salt in, keeping the levels "ideal" as the tester read. I removed the "healthy" other fish from the tank and all the decorations and fake plants. Tonight, I came home and he was floating, not moving, not breathing.

My question is twofold: what do you think my fish died of and what should I do with the tank and my "healthy" other fish?

I am concerned that whatever my dead fish had may have gotten to the other though there are no signs of illness in him and I am also concerned about how I should clean/prepare the tank so that I can put the other fish back into it.

Thanks for all your help - I know I am long-winded, but this is my first tank since I was a kid and losing my fish really upset me! Any advice you have will be much appreciated!

Sincerely,

Lauren

Answer
Hi Lauren;

I'm so sorry you lost him. It is hard to lose our fishy friends.

There is no way to really know for sure why he died. It may have been a bacterial infection and got better from the medicine but maybe he still had internal issues you couldn't see. The other fish was already exposed to whatever it is so I don't think he is in danger. I would make a 50% water change to reduce the medicines and salt and just put him and the decorations back in there.

I didn't see a reading of the toxin "nitrites". I saw that you tested the nitrAtes but they are different and will not be elevated in such a new tank yet. Nitrites are elevated at about the 3 to 4 weeks stage after you add your first fish. They can be deadly and actually cause the symptoms described. If you could get a test of that it would be helpful.

At Your Service;
Chris Robbins