Aquarium Safe plastic for rock casting?

GDominy

Bottom feeders Rule
I am building a custom 6 foot "back to nature" style background for my 135 gallon loach tank. I will be casting an entire wall of slate in 2 foot sections (so I can get around the center brace) and "hanging" them from the back wall of glass. Its difficult to explain, but the three pieces will fit together like a puzzle so you cant see the joining line (easy to do with slate).

I already have designed the form for the rock wall pieces and I have the sand and slate required to make the wall I'm going to cast. I've found the casting rubber I'll be using to make the mould for the wall as well as the strengthener to back it up.

My problem; What am I going to make the wall out of?

Concrete will be too heavy, the local plastics store is telling me that Epoxy is toxic (they were sued because a Koi farmer used it and killed off over 2.5 million dollars worth of Koi. Its safe for humans, but not for fish).

I need to make this casting lightweight, so I was hoping to use some form of plastic resin... Any idea's?
 
you could remelt old milk jugs, you just have to be careful to not to get it to hot. wax might even work if you dont have plecos. I believe most epoxies are safe after they are cured and rinsed well. i have used several types without any complications on snail shells that where deteriorrating.
 
I certainly wonder why someone would add a large amount of epoxy to a pond with $2.5 million dollars of fish in it..

Wouldnt you think you would test a small amount first?
 
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