what to feed my fish

Hello,
I am a newbie here. I have a total of 6 fish:

2 - Large Goldfish (About 5" big right now)
2 - Pleco's
1 - Black Moor (About 2-3" big)
1 - Hightail/Fintail Shark

I have a couple things of food but, I dont know which combo of food or single food to feed them. I have:

Goldfish Pellets. My GF love these and practically jump out of the tank to get them.
Sinking Shrimp Pellets. I was told to give these to shark because he is a bottom feeder.

When I feed with both, all the fish usually eat one or the other and its never the same. Sometimes, the food gets left in the tank because they dont eat. Does anyone have a better idea of what I can do? Or, maybe something new I havnt tried. I dont want to overfeed them because I think they are not eating; but, I dont want them not to eat the food I give.

Any help would be great, thanks.