A protein skimmer will help alot. As far as filtration u might want to go with a sump/refugium. Im not sure how much room you even have under your tank in the cabinet. You can either buy these premade of make one urself. Maybe you could turn your old 20 into a sump? but i dont know if you could fit that in your cabinet. making one is easy. All you need is aquarium silicon and some plexiglass. Then you could put your protein skimmer down in the sump. But being a 36gallon tank im not sure if you could get a hang on back skimmer and just do weekly water changes? You will have to let the experts decide on that `1`