Aquarium Safe plastic for rock casting?

[GDominy]

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?

[BK]

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.

[slipknottin]

Use the right epoxy and let it dry and its perfectly safe.

[wetmanNY]

Epoxy sets hard long before it's cured. Once cured it's inert. If the two resin and hardener elements aren't thoroughly whipped together perhaps, the result might never cure right.

I'd reserve judgment on the suit tale.

[slipknottin]

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?

[GDominy]

Well, if I were the pond keeper I definately would have tested it first. I remember the lawsuit, it happened a few years ago with one of the koi farmers in BC, they had a short piece on the news about it.

Are there any brands of Epoxy you can recomend?

[slipknottin]

Sweetwater is the only name brand I know of.