Bill,
I would go with a black plastic mesh that is available from many aquaculture suppliers. If you can't find one let me know and I can advise. Many will sell it by the foot, and it typically is about four feet in height. The plastic will last longer, is nontoxic(I believe hardware cloth is galvanized), not as rough on the fish as hardware cloth, and easy to work with. I've had some cages for three or four years and they are still holding up fine.
I use 1 1/2 inch pvc glued together for the frame, and lash the plastic mesh to it using lock ties available at any hardware supply. I would suggest joining the corners with three way pvc connectors which you may have to find from an aquaculture supplier. I drill holes in my pvc so it will fill with water weighing it down but attach clorox/orange juice containers near the top that have their lids glued on to float the cage. Attach them so the top of the cage is above water about 8 inches to keep the fish from jumping out. I used to attach brown tarping to the corners for shade, but I now use piece of builders styrofoam billets for shade as it is more rigid. I drill holes into the foam and put air hose or surgical tubing in the holes for the twist tie to go through to prevent the foam from tearing in the wind.
As far as mesh size, go as large as possible as algae will probably build up on the mesh. It's imperative that there is good water flow through the cage and there is at least two or three feet of water under the cage above the bottom. If you would like to see a picture of one of mine email me at
[email protected].
