Slower is better, although I can't tell you the exact rpm. If it is too fast, the whirlpool will cause more of the silver to accumulater within the pool than throughout the entire container. This whirlpool can be very near the electrodes, further causing the electrodes to build up deposits. Look at the Cynmar "Lil Stir" magnetic stirrer. Its about $20 and does a very good job on containers of 1 quart or less. The Silvergen SG6 barely moves the water at all. In fact, I thought it was not even working until I inquired about it.