Two Little Fishies KW Reactor 300 Check Valve Part# E
 
NOTE:  This replacement part looks different than the stock part that comes with the Reactor 300 but functions the same. The one pictured in the Operating Instructions looks different but this replacement works. Unfortunately, this is the only replacement Check Value available from Two Little Fishies. It will work with 1/2" ID hose so you may need to make a few minor adjustment in your hosing.