Ok we need to stop the non-sense about Bio III being "good DoT for solo kiting", it's not. It's DoT effect is based entirely on dark magic skill, something RDM gets a E in and has 300 native skill @99. /SCH DA will bring you to 404 but then your not having blinks and stuck juggling LA / DA while running.
http://wiki.bluegartr.com/bg/Bio_III
That's 13hp/tick at naked 99 RDM, 17 as a 99 RDM/SCH with DA up. It takes 27 dark skill to raise it my one point so your looking at ~20/tick tops.
The real issue is it's duration, at 30s it's pretty much useless. You need 4/5 to get any form of use-fullness out of it, and 5/5 for it to be worth the MP cost. This precludes you from picking other, more important spells. While you can Sab Poison II then toss out a Thunder IV for better damage. And with how much enhancing magic RDM has, standing toe to toe and meleeing things to death is typically a far better strategy.