My goldfish was pooping this very long white flat poop and now it hasn't pooped in about 4 days. He is sitting at the bottom and the bottom of his body looks red and streaky like blood (but no blood in the water) In the tank we have 2 large goldfish (he is one of them) 1 catfish (been in tank a long time) and a new 3" Pleco. any suggestions?

Optional Information:
Age: 11; Breed: goldfish

Already Tried:
nothing