Are these your tank's occupants right now?
2 goldfish
3 corydoras
4 sunset platies
6 tiger barbs
5 serpae tetra
4 clams
If so, I'd recommend doing something about those goldfish. Some species can get really big, and all of them are messy eaters and coolwater (as opposed to tropical, like the rest of your livestock) fish.
You might, eventually, run into problems with your tiger barbs, too, since they're pretty nippy buggers and might give their tankmates a hard time.
If you do get rid of those goldfish, whether by getting them a tank of their own (it's easier said than done, eh?) or by giving them back to your LFS, you can easily get 5 or 6 otos in your tank. When they're in a shoal, they're cute little monkeys, when alone, they'd probably be less amusing than your clams are currently.
If you can't/don't feel like getting rid of your goldfish, getting a few otos would bring you pretty close to, if not over, maximum stocking capacity. One thing that works is an algae scraper, although they're nowhere near as cute...
Hope that helped, let us know what you decide to do.