I bought the azoo C02 check valve after I received a little shock from the C02 solenoid. The Co2 check valve on my Coralife Ca reactor 500 gave out and was letting saltwater flow back into my C02 solenoid causing a drip when I went and check the solenoid I got a zapped, not a good thing. I had to shut down my reactor and find a new fast. I placed an order with AquaCave and with their fast customer service and shipping I received the Azoo check valve in no time. The Azoo Co2 check valve is a lot better then the check valve that Coralife put on. With the Coralife valve you can blow in the discharge side of the valve and feel a little resistance and a little air will make its way through but worked to hold back reverse flowing water but I knew it would give out eventually. 3 years later it finally failed. The Azoo check valve is built way better and trying to blow through the end was futile. The co2 has to build up enough pressure to be able to open the valve and to start dosing Co2 into the reactor. The Germen ABS check valve is built better but more expensive and at times will close and stay closed until either enough pressure builds up to open it or you have to tap on it to free it. All in all the Azoo is a good cheap replacement valve that is worth the money.