The tank is not heated unless it gets chilly in winter - I live in San Diego and the tank is almost always stable at 72. I sometimes have to add treated ice in the summer to keep it down below 75. I have 3 fan tails and 1 moor who all do fine in the 55 gallon at that temp - the worst ailment any of them have gotten once out of Q from the store is a minor case of fin rot, which went away on its own after a routine water change. I monitor and change their water regularly, so they're in no danger of poisoning themselves unless something terrible happens to me. I have a sponge and re-fillable cartridges of activated carbon in a Marineland HOB filter with a (what I believe to be somewhat useless) bio-wheel.
As for the plec, he's never shown me any sign of stress at 72. He's also a well fed guy - zucchini, blanched lettuce, peas, frozen greens from the LFS, a hoagy-sized chunk of driftwood, AND whatever he finds at the bottom in the way of flake food. He might go a day or two without a chunk of something like zuc to suck on, and that's when he might be going after the plants. But I'm not even certain which of the fish really is the culprit for uprooting the plants or eating them, so I just implicate them all. Anacharis never lasts long with them. At the moment, he has two ridiculous halves of a "sunken pirate ship" that came with the tank when I bought it, and he has claimed both of them as his territory for hide-outs. I have been trying to find suitable wood to replace it because I hate it, but I leave it in the tank in the meantime because he likes it. The tank is forever a work in progress, and the right wood (that doesn't cloud the tub) has not come to me yet.
My goldies and my plec are all between 1 and 3 years old, so they are far from full grown. I understand about tank size, filtration, overcrowding... they are well loved and will be taken care of. I also understand that some plecs are aggressive - the only time he shows any aggression as of yet is if one of the goldies goes after his cucumber while he's sucking on it, then he chases them away and goes back to it. The moment I see him go after them unprovoked or see evidence on any of the goldies that he's attacking them, the situation will change.
I hope that quells any fears about the well-being of the fish involved.
My lights are the two fluorescent tubes that came in the hoods when I bought the tank used. They are certainly PLENTY for the hornwort, it grows like a weed and reaches the surface in what seems a matter of days, then I re-distribute it and it sends more runners up to the surface. Half of the tank is becoming somewhat of a hornwort forest. It looks neat, but I'd like some variety, of course, and color would be awesome! The small (amazon swords? i think? i never know with my LFS) do okay, but they often look like the plec has sucked pock marks in them, though I've never seen him doing it. I always assumed he was eating algae off of them, and was overzealous. The only other plant is a tall grassy-looking thing that has a ginger-type rhizome at the base - it's longest blades are up to 11 inches long at this point. The tank is 24 inches deep. I'm hoping to find plants that will be happy without additional CO2 or ferts and that aren't "tasty." Thanks everyone for all of the suggestions!