rust on leaves?

[BobBong]

Pics and conditions, especially soil runoff pH or res pH if in hydro. Fill out the troubleshooting form and post the info. It's at teh top of the section.
K def is a likely suspect for a rusty appearance. Common in wet, acid soils.

I've also understood that a P overdose can look alot like a K def.. what do you think?

Without any more info it's hard to say anything for sure though.