+1 on the weak bleach solution... Let it soak in there for a few minutes then rinse with fresh water.

I ran into HEED the first time last weekend... organizers at one of the early summer centuries got some sponsorship from Hammer, so they put HEED in the energy drink coolers. I drank two cups of it at the second rest stop, and most of one bottle over the next 30 miles, and wound up cramping like crazy... not to mention a little nausea. Could have been that I was hanging with a pretty fast group, but the cramps lead me to think it was the electrolytes...

I'm a big fan or Hammer gels, but I think I;ll leave the HEED alone for the time being.'