Iodine for biocide?
 

I was thinking, would Iodine be a good biocide in liquid cooling? Would it affect the metal in anyway?

It should, theoreticaly. I've heard that betadine works in a loop. frozenCPU has stuff that's for sure safe in a loop.

Why not just use alcohol or a little antifreeze? Both are quite toxic to microbs and won't hurt metals. Not to mention they're cheap and do not stain things like iodine does.

Sure, both are toxic. But alchohol isn't pure, it has other things in it and isn't designed to recirculate constantly and MAY break down.. Plain antifreeze may be a better option because it's close to what most water-coolers use anyway. Either way, I wouldn't dismiss dedicated algaecides being that they're known quantities. Plus, it doesn't really make sense to spend $300 on a loop and then blanch at $5.00 for algaecide that's designed for its intended purpose.