i have never experienced what u just have.
i use some cheap WW knockoff (alentra radiator protector). should work against leaks, corrosion. looks really foul.
to that i add a couple of drops of dishwashing agent. that should take care of surface tention as stated by swiftech. over here i read some good stuff about dishwasher in the "chem of coolants" article by Brian.
chk it out if u haven't already, u r sure to find some ideas in that article.
http://www.procooling.com/articles/h..._coolin1.shtml
however, i do flush the system every 2-3 months, with an assortment of hydrochloric acid, vinegar, bleech, whatever i think is real nasty against algae, and i have lying around. bleech and hydrochloric acid is supposed to oxidize metal, but if u leave it in for about 5 mins, i don't thk it is gonna do that much harm.