I was always wandering what is real water flow of my canister filters. Solution - built a flow meter based on arduino.
arduino Uno (~$5)
Water flow sensor flowmeter ($3.50 from that site)
Bluetooth HM-10 (AT-09 BLE Bluetooth 4.0 Uart Transceiver Module CC2541 Central Switching HM-10) $5
some wires and miscellaneous parts
The schematic is very simple, as well as the arduino code. Can provide if there is interest.
A simple version is to use just the flow sensor, and read the serial on the laptop.
With HM-10 you can see the results on an iDevice, via a free app LightBlue.
Eheim 2217, 130 gph (manufacture reported flow 208gph)
Eheim 2215 with a CO2 reactor (this https://www.plantedtank.net/forums/15...clear-pvc.html
) , 81 gph (manufacture reported flow 134 gph)
I am just reporting the numbers, and not implying anything