| try C and R lou there a glass supply company they sell aquarium silicone in bulk. I'm not sure if thats the correct spelling though.I would use at least 3/8 glass if not 1/2 inch. I don't think 1/4 would be a good idea. I'll try and look up the catalog next time I'm at work. the average price is 25$ a square foot for 1/2'' starfire but you could use cheaper glass for the back.
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Matt
150 gallon mixed reef
55 gallon refugium
100 gallon sump | 
