I have two small clowns, a small regal tang, a medium sized purple tang, a cleaner wrasse and a lawnmower blenny in a 150.
After a good talking to by Keith over at Aquatic Design, I'm a believer that fish need a lot less food than I thought. He contends, and I agree, that just because the fish will consume everything you put in a tank in a couple of minutes doesn't mean they're hungry, that it's good for them to eat like pigs all the time, or that they're not just pooping it all out all over the tank instead of digesting it properly and converting it to energy.
I feed my fish a variety of foods, every day, and sometimes it's not every day but every other day... nori, squid, mysis, frozen brine and live brine and raw shrimp, no cocktail sauce... they just don't like it with sauce.
What I am doing now is to soak the food in Marine Zoe. This stuff is absolutely wonderful for keeping your fish (and inverts, corals, etc.) colorful, happy and it keeps them from getting diseased or parasitic. My buddy turned me on to Zoe years ago and I've been a fan ever since.
Zoe may be expensive, but I had a yellow tang and a maroon clown get large and fat with it and live in my tank... with five tear down and moves mind you... for seven years. And I only do water changes about three times a year.
My motto: Feed sparingly with excellent, vitamin enriched food and duplicate the ocean the best you can...