Is this plummets putty ok to use?

Noooooo! Thats an oil based putty that never gets totally hard. You need to use an epoxy putty.
 
Many of the epoxy putties intended for plumbing repair have metal content. Personally, that makes me nervous. I've used the JB Weld brand putty (waterweld I think it's called - the MSDS for it looks pretty clean) but considering you're only saving a buck or two over putties intended for aquarium use, personally I don't think it's worth it to risk things.

If you do want to try a plumbing product, I'd check its MSDS before using it.
 
I actually have a stick of that (for use on home plumbing) and don't see anything on the label about aquariums. Can you specify exactly which product you're talking about? i.e. which size/packaging/model number/etc.?
 
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