Monthly upkeep costs for your system?

[Aquattro]

Last time I calculated total annual cost divided by 12, it was about 127.00/mo for a 150g running 400w MH lights. All costs were considered, RO membrance replacement, bulb costs, hydro, water, food, test kits, etc.

This did not take into account replacement parts for pumps (impellers), but that's minimal.
That number though, can vary greatly, depending on your setup and equipment.