Reefers, what do you AVOID adding in your tank because they may hurt your corals?

[asylumdown]

I would extend that to a blanket 'everything I didn't pay for'.

I break all frags and corals off their base rocks or plugs and throw them away. I aggressively clean (and sometimes bleach) the exposed skeletons of LPS. Rock from other people's tanks/tanks at the LFS are very effective vectors for problem algae, flatworms, and all sorts of other things I don't even know about I'm sure.

Other than that I don't really avoid anything other than fish who include coral as a primary part of their diet. I also won't buy any softies like toadstools because this reef is mostly SPS and I've heard they can go to chemical war.