I used 1/2" OD but if I order anything else I would order some 3/4" to build another that would float a little higher out of the water.
Extruded Square Acrylic Tubing | U.S. Plastic Corp.
I also bought the acrylic glue and other acrylic pieces that I use from here. They hav good prices on all acrylic pieces but the shipping can get expensive with the larger pieces. I also get the acrylic adhesive SC-125 and use the syringe applicators.
With thicker rod, won't it sink more than float since it is heavier?