Selcon is a vitamin supplement used mostly for fish. They recommend that you soak fish food in the Selcon, or feed it to live brine shrimp to increase their nutritional value before feeding to the fish. Not clear if Selcon in the water column aids corals.
Fuel is a blend of amino acids, vitamins, fatty acids, and carbohydrates intended to be dosed in the tank to enable coral growth. Since it is suspended in the water column, fish will get minimal, or no benefit from fuel.
BTW, I am hearing of algae and cyano outbreaks in tanks dosing Fuel heavily. Caution is encouraged. Another alternative for corals is AcroPower, which contains only the amino acids.
Hope this helps,
Jim