Is regular marine epoxy safe?


I can't find aquarium epoxy in any Pet stores by me. I don't want nor can I afford at the moment to order $100.00 worth of stuff on the internet to put it with another order.
Just for epoxy I would pay more for shipping than the money for the putty.
Marine putty that I found in the hardware store looks like the same thing and I would like to use it because it works underwater so I can attach my corals so they won't fall.
I don't know how I made a double??? How do I remove this extra thread????
Is it safen to use???