Actually, SOME people have very bad reactions to chlorella (info in the yahoo chelation and autism/mercury groups). It certainly made me feel extremely wired. Having said that I have read some posts where parents say chlorella HAS helped their children.
In chemistry terms though it's not considered a TRUE chelator and some brands can be contaminated with mercury anyway as it absorbs it from the environment. Just because it's natural doesn't guarantee its safety. Here are some of Andy Cutler's comments on chlorella.....
As for DMSA, yes it could be dangerous IF you take too much of it and/or take it at random times, or it just doesn't agree with you (as with me). However it DOES chelate mercury and is considered safe if used correctly.
If you're doing fine on chlorella that's great but be careful :) Don't want to worry you or cause anxiety for anyone!! :)