Water flow meter??

[Myka]

I'm trying to find a flow meter that I could put either before or after a reactor to measure the GPH through the reactor in the range of about 50-200 GPH. It will be on a reactor that I will be turning up and down, so I don't want to do the old fashioned timed water in a bucket method. I can't seem to find anything non-metallic though. Anyone know??