Honestly I don't know. I've seen people write on their frag plugs to indicate the name of the coral on the plug but never considered how safe that is. #reefsquad
Probably no one has actually studied this question, but I'd guess it would not be an issue.
Tiny amount of material diluted into an markedly larger water volume, even if some did come off.
Also unlikely to be any highly toxic materials in something that kids could put in their mouths, etc.
Hey everyone, So I noticed in a lot of the selling post that people are using permanent marker on the plugs. Are normal markers safe or are they a special type? Thanks, Dan