the red stuff is dead algae..call your local water department and ask about it...turn your tank temp down a bit if you can, it won't hurt your fish yet, keep up the water changes. The reason I know this...there's a widespread problem with red algea...EVERYWHERE in the world because of global warming. YOu might want to have your tap water professionally tested. YOu can buy stuff at the fish store(not a chain store) to remove it but I can't think of the name just now. Your pleco will most likely be the first one to get sick so keep an eye on him.
AND you can too keep goldfish with tropicals..the main problem with goldfish is that they are dirty fish. My first tank was a 15 gallo...with 2 black tetras, 1 redtail shark, 2 swords a pleco, a calico cory, and 1 goldfish and they lived together for over a year untill the goldfish got too big. Oh yeah and my puffer had a tank buddy who for some reason he wouldn't eat for 6 months by the time he got around to eating it , it was too big for him to eat.. Yes he ate other goldfish but not his buddy(wierd creature)
AND you can too keep goldfish with tropicals..the main problem with goldfish is that they are dirty fish. My first tank was a 15 gallo...with 2 black tetras, 1 redtail shark, 2 swords a pleco, a calico cory, and 1 goldfish and they lived together for over a year untill the goldfish got too big. Oh yeah and my puffer had a tank buddy who for some reason he wouldn't eat for 6 months by the time he got around to eating it , it was too big for him to eat.. Yes he ate other goldfish but not his buddy(wierd creature)