I think (my memory is so bad!) that I used to strap two 2 kg weights to my unit, one on each of the cylinder bottoms, so 4 kg all in...which doesn't seem that much to me I have to say...
However, I can't for the life of me remember whether or not I used a weight belt as well.
What do you guys need?
(assuming drysuit diving)
Thanks in advance for your assistance!