Keep in mind that RT's are omnivorus and scavangers for the most part. Basically he's a meat eater that likes a salad every now and then.
I doubt that he is only eating algae when he is skimming over your plants. He is probably also picking up small pieces of uneaten food that he finds that happen to have fallen on the leaves.
I doubt unless he was really really hungry that he would even look at the algae tablets. It is very hard IMO to starve a Red Tail. He will find food.
I guarantee that if you stick any sorts of good food in there he will eat it. Especially frozen stuff or a good quality flake.
Count your lucky stars that he isn't aggressive when feeding time comes. Your fish wouldn't stand a chance. I've had a couple of RT's that would chase away my cichlids from the food because he was such a sob at feeding time.
As for your RT not bothering you Gourami. Chances are that it is because he hasn't seen the gouami as a threat or challenger yet. Give it time. They will have a scrap sooner or later and the RT will be the Instigator.
