The dwyer meters and similiar types are NOT entirely accurate for measuring skimmers air draw. When RE puts out the numbers they are from measurments with a different type of air measurement device/meter that is more suited for the purpose. If one cares to search through the thread, Klaus states what device he uses to test his skimmers and derive the air draw numbers.
If you are comparing numbers with Jeremy, then that is fine, for reference purposes, IF you are using the same MODEL (not just brand but brand AND model) meter that he is using. Just like I stated, my RMA and my RMC will take two different measurments of the same skimmer. My RMA has smaller intakes, through port and output than the RMC and restricts the flow much more. Both meters restrict the skimmer pumps air intake, (the RMC has 3/8" threaded intakes and still restricts the flow). ... it is perfectly logical that NEITHER will give a truly accurate measurement. But they are perfectly fine for my own reference or reference against another same brand and model meter. But I wouldnt take a measurement with my RMA and expect it accurately match that of someone elses RMC or RMB or another brand and model of air flow meter.
That said, and not to re-open old issues but the 200 that you returned measured as Jeremy expected and was working perfectly when Jeremy tested it. The meter he used measured the air draw that he was typically measuring with properly performing Alpha 200's which was, if memory serves, several hundred LPH over what yo reported here on the forum. And the pump was not surging. He would never have offered it for sale in this thread and re-sold it if it did not perform as it should.
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kvmn ... I dont know if removing the ozone tube will change the numbers you measure on the main air line. You stated that you were measuring 300 LPM, or whatever it was, through the ozone tube so I figured it was worth a shot to remove it and measure just the main air line since it seems logical that they could be sharing the air to some degree.