Feeding?

i have 13 fish in my 100 gallon tank. i have 5 chromis, 4 diff types of sweet lips, 1 unicorn tang, a bicolord angel, and a pair of false percs.
how much should i feed, every time i finish feeding i feel like they still need more i feed one brine cube a day.;D

 

Thats all you feed is brine? Brine has little nutritional value. It is also important to note what types of food a particular species of fish needs.
The chromis and clowns are omnivores, and will need both meaty and seaweed/veggie diets. The tank will be an herbivore, and needs massive amounts of veggie/seaweed (they will often take meat though). The pygmy angel is an omnivore, and will again need both meaty and veggie diets. It will also need a diet specifically targeted to angels that is fortified with marine sponges.
It is very important to feed a variety of food of a proper nutrition for each species of fish or you will always have health or disease problems with the fish. Brine is OK, but nothing more than that. You will get much better results from mysis. How much is really a broad area and can depend on too many factors. Feed just enough to keep the fish plump and healthy but not to polute your water quality.

 

Well in my experience with chromis, they are pigs period. Mine always beg for food even after I have just fed them so get used to that

In regards to food, I would definitely feed a better variety of food and feed more than 1 cube a day. Just like packleader stated, brine is OK but does not have the proper requirements for your fish. At least get spirulina enriched brine the next time you purchase because it is better for the omnivores. I would recommend mysys as well but it may take some time for the fish to eat it since they are used to the brine so you may have to slowly introduce the mysys until they get used to it. I also soak all my foods with selcon before putting in the tank to gut load the food with vitamins and essential fatty acids required for the fish.

Also with the tangs, there are a few different herbivore preparations out there and you should hang a veggie clip with seaweed for them to eat too.

here are some you may want to try for the herbivores and angles:

Aquarium Fish Foods: San Francisco Bay Brand Angel & Butterfly Diet

Aquarium Fish Foods: Ocean Nutrition Formula Two Frozen Food

As far as amount and frequency, it's better IMO to feed small amounts more frequently than one large feeding. Depending on your daily schedule, if you could do 2 small feedings a day that would be better to control the amount than 1 large feeding and less of a chance of polluting the tank.

It's trial and error IMO - you need to do what works best for you and your fish