need help please

[Solarris]

I just had a pleco I purchased a couple days ago die in my quarantine tank. I'm not really sure what he had. less than 2 days after I bought him I noticed his fins were looking kind of bad, maybe fin rot, not really sure. A couple hours later I checked on him and he was dead. He looked like he had a skinned area on top of his head when I looked closely and his fins looked really bad. I don't think it was ich because I saw no white spots on him at all. I've decided not to add a pleco to my tank now because I haven't had any luck with them at all and I don't think I need them since I don't really have any algea on my tank. Now I would like to set my quarantine tank up as a home for a blue lobster but I wasn't sure if it would be safe to now. Could whatever made the pleco sick be in the filter sponge? I have an aquaclear 20. I haven't moved the filter sponge into my big tank because I'm afraid of infecting my other fish. Should I just get a new sponge and let it sit in my big tank a few weeks first? Also, my filter sponge doesn't really fit in my big filter, a marineland 400, so would just letting it sit on the bottom of the tank be enough to populate it with enough bacteria that I wouldn't have to worry about a cycle when I put it back on my other tank?

 

[patola_l]

1. Id test your water and make sure nitrite and ammonia are at 0 ppm.... im willing to bet that the issue was already started at the pet store. it doesn't really matter if it doesnt fit, even if it floats in the Hang on filter it will work. Or put it where the water come out the filter so it first hits the sponge