I have the Red Sea Reactor 500 and when it runs it does a nice job. Unfortunately about every week or two my timer kicks in but the pump does not go on, needing a nudge or a in-and-out on the plug and then it starts up. But sometimes I do not notice that and it's a full day with little to no CO2 diffusion in my tank. Nothing better to encourage a nice BBA bloom....so I've stopped using it. Too unreliable in my experience.Maybe the Red Sea Reactor 500. It works well (99.5% diffusion), and is fairly easy to hide. It also works with DIY CO2 if you need it to.