Hello, so a while ago I had a tank with a blue gourami fish and a couple mollie s. My gourami had this long white stringy poo from the start when I got him, and he soon died and it spread to the rest of the tank and whipped them all out. I looked it up and think it could internal parasites. Anyway, I recently got a new aquarium, bran new aquarium, bran new rocks, bran new fish, etc. I got rid of all the other rocks, not wanting any chance of these parasites getting to my new fish. Today I bought a twig catfish, (this is my very first time having one so if anyone has any basic care tips feel free to share), but not 10 minutes after I put him in the tank with my two mollies did I notice that he has this long line of white stringy poo. What is this and how can I get rid of it? Somebody please help! Other details, my algae eater is the only survivor from my previous fish epidemic and I have him in his own separate tank away from these new fish just in case he has it too. After seeing the white stringy poo, I put my twig catfish in with him as quarantine to prevent it from spreading to my mollies. Was this a bad idea? What else can I do?