What bug is this?
 

Last night I picked up a snail that was on my frag. While lifting it up I saw 3 bugs run around super fast. I took a pic quickly. It's the orangey bug on the rim of the plug and under the rim in the 2nd pic.

http://i1292.photobucket.com/albums/...psii30pads.jpg

http://i1292.photobucket.com/albums/...psxn6jtxr8.jpg

Hard to tell. Looks like an amphipod.

If it has 12 legs, some antennae and some rear gear, it's an isopod
Long and thin little guy. Fish nummies

http://www.melevsreef.com/id/safe_isopod.jpg

Better hope it is not a flatworm...

I wasn't able to count the legs I will look next time. Are flat worms fast? Cuz these guys were FAST!!

a fast flatworm is one moving fast enough to clue you in to the fact it's alive. Def not a flatworm.

+1. I thought the flatworms in my tank were coralline algae for months.

Flatworms mosey along at a snail's pace
Fast would indicate pods
From what I could see in your second pic, it looks like the pic I posted

Let us know

the pic u posted seems to be a clear lookin bug.... mines more orangy red

They look more clear in macro than they are to the naked eye. They're small enough that what colour they appear to be can be dependent on what's in their stomach at that particular moment.

In any case, none of the scary things that you need to worry about look or behave the way you described as far as I know. It's not a flat worm of any kind, it's not a nudibranch (coral eating or otherwise), it's not an acro eating 'red bug' as a) it wouldn't be on the plug and b) they're way smaller and shaped different, and it's not any of the other nasty snails or, worms, or starfishes that are known to cause problems. Even if it's not the exact type of pod from the picture, it's more than likely just one of the many beneficial/neutral microfauna that you couldn't keep out of a reef tank if you tried. I can count 5 different species of tiny crustaceany pod thingy hiding between the glass and my frag rack right now.