Further to what Nursie and Galaxie advised:
Not only do they have different temperature requirements, but they also require different food.
The pleco will either starve to death or start sucking on the goldfish's slime coat (as Nursie pointed out) and kill it. Seriously. Anything you throw in the tank, the goldfish will eat. Algae wafers, veggies, it doesn't matter. The goldfish will eat it before the pleco can get anything decent in his stomach.
A scrub brush is good for algae, snails are good for algae.
Roan
Not only do they have different temperature requirements, but they also require different food.
The pleco will either starve to death or start sucking on the goldfish's slime coat (as Nursie pointed out) and kill it. Seriously. Anything you throw in the tank, the goldfish will eat. Algae wafers, veggies, it doesn't matter. The goldfish will eat it before the pleco can get anything decent in his stomach.
A scrub brush is good for algae, snails are good for algae.
Roan