Hi Francine. Most major aquariums have their rockwork built by a handful of rockwork companies. Most of the rockwork is cement with fiberglass reinforcing. For some applications solid epoxy and fiberglass epoxy combinations are used. Styro foam is used for filler under cement where detail is needed, bricks and cinder blocks are used for filler in other applications. Most of the epoxy types are very expensive. If you use cement you'll need to acid bath cure it. ------------------------------------------------------------------------- This is the apistogramma mailing list, apisto@listbox.com. For instructions on how to subscribe or unsubscribe or get help, email apisto-request@listbox.com. Search http://altavista.digital.com for "Apistogramma Mailing List Archives"!