I have used both models of the Tunze ATO for a long tine without any problems. At the moment I’m using two tunze Ato Nano and one regular ATO with the optical lense for larger setups. I been out of town a couple times for one-two weeks at a time with positive results. The only thing that I dislike about these is that the pump is loud when it operates, but usually it only runs for about 10 seconds at a time.