(03/25/2006) - I've used this CO2 controller for 4 years. Just recently, the display stopped showing the correct value. However, it still turns on and off at the correct pH points. I have verified this using a separate pH monitor. There is a very large downside to this controller. It requires a 0.2 swing in pH. The pH swings 0.1 below and 0.1 above the set point, creating the 0.2 swing. This is a large swing value and could mean the CO2 saturation level will be below or above the desired CO2 ppm 1/2 the time it’s controlling the injection. For example, a KH of 7 and pH controller set to 7.0 and 7.2. CO2 saturation will swing from 13ppm to 22ppm. 25ppm can be stressful to fish and below 17ppm is less than ideal. If you could limit the swing to 0.05, this would allow the controller to maintain CO2 saturation at 18ppm to 22ppm. This would be perfect. However, the Pinpoint controller does not offer this. The controller requires the CO2 saturation point down to 13ppm before turning back on, due to it’s very large swing value. I called Pinpoint years ago when I first purchased the unit. They offered no solution in reducing the swing value. All in all, it has been a decent controller. I would recommend it to those who need a cheap controller. If you’re looking for optimal plant growth, I would highly recommend purchasing a different controller with a smaller pH swing value.

(06/01/2004) - Very good product! The only drawback is that the PH has to fluctuate by .1 when dosing CO2