Maybe a school of Brass Tetras?? They school higher in tank.
Hey guys, finally almost done stocking. Right now it's at 5 red eye tetras, 5 peppered cories, 2 south american bumble bee catfish, and one farlowella
DO IT! DO IT! DO IT!
It's probably just the plastic/vinyl becoming discolored. Is there any UV light or sunlight hitting the tubing? This used to happen to clear t-shirt bags