Those paint balls are .12 grams and about the tanks power if it is that strong and you want it weaker wich may be a good thing it will last longer just use the Air duster cans they come in ywo types A143 strong and 152 weaker power you can probably get this thing down in the two hundreds FPS marke with your choice of propellent you use to power the gun.
I would do some testing and FPS reading in a video using the different type propellents to power the gun when i do get mine.