8O powderblue, dont go offering advice when you dont know what you're talking about. Clown loach adult size is 10-12", much to big for a 20g. I dont think ghost shrimp eat much algae, but I've found amano shrimp to be great algae eaters. You could do 6-10 shrimp and they should be able to keep the algae to a minimum. And some plecos dont do so well in planted tanks, they can be clumsy and uproot plants and knock over stuff. :?
*Edit - Aquariumfreak, clown loaches dont eat algae, but they'll eat peices of food that others miss.