Jill, you might want to start posting again on the Lantus/Basaglar/Levemir forum for dosing advice. It's a much more active forum and with plenty of people who can answer in a more timely manner.
You can try 10.0 units. It's be an opportunity to see how sensitive he is to this size of dose change. Usually over 10 units we make changes by 1.0 units at a time. With a recent change in cabergoline in the picture, you will have to keep in mind that you may need larger changes. But let's see if this is a on-off or a trend first.