Need opinions on frag plugs

[howdy20012002]

hey all.
I am going to make a few hundreds/thousands of frags plugs and wanted to get some advice from people
first, what size would you make them?
I was going to use full size muffin tins and mini muffin tins and pour the concrete into the approx bottom 1/3 of the holes.
do you think a plug about the size of a toonie is better or one the size a bottom of a muffin.
it would be for various corals.
as well, does anyone know what kind of cement to use?
and any suggestions for dying the concrete.
I would like to be able to label the corals as being from me...any suggestions how to dye the concrete.
thanks in advance
Neal