i think you will be fine drilling and chiseling the LR. i know a lot of people do it when using PVC as a base structure to hold up the LR. if the LR is all dried out any way the risk is even less. most of the tools are steel. the iron in the tools may give you a bigger algae bloom, but i do not think it would be really noticeable.
hth,
G~
hth,
G~