They grow faster with bright lights, CO2, etc. Mine have grown faster too under good lighting.. without CO2. I can see the difference, especially when I pick them up to squeeze them out. You can feel they get heavier too. But even under low lights with no special care, they seem to grow faster than that. I just listed what is commonly reported as "average" growth. Try not to overstate things where someone will end up being disappointed if they don't get the same results.
Have yours produced any new balls yet, Customdrum?