I'm sorry about your loss. I don't think it was parasites. I think Melody is right on in that the tank wasn't cycled and there were issues with water quality. How are the rest of the inhabitants? I'd do much more than 10% water changes and be sure to get the liquid test kit. And don't be sad about the upgrade, the fish will be happier in the long run once the new tank is cycled. I'd also use Prime to help lame the nitrite and ammonia less toxic until you get the tank cycled.
Edit: I have to agree with Melody in that the fish you have are going to get much too big to be all together in a 110 gallon. Eventually this will lead to more illnesses and poor water quality.
Edit: I have to agree with Melody in that the fish you have are going to get much too big to be all together in a 110 gallon. Eventually this will lead to more illnesses and poor water quality.