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*ACTUAL*flow rates. We all know that a canister (or any Powerhead) has a max head height for which it remains effective. What I need to know is some sort of formula for calculating flow/pressure loss over a particular height, through a particular diameter of hose...

An example; I buy a Canister filter with an advertised flow of 700lph, and max head of 1.8m. It sits in a cabinet approx. 600mm below the water surface and flows thru 17mm pipes. What is the actual flow felt by the little fishies in the tank? Variables to ignore: spraybar hole size; level of gunk present in the canister...

Finally, I intend to DIY an inline CO2 diffusor at some stage. If I have in mind a canister that will see a (advertised) flow of 500lph, would I be best to go to a 550 or 600 to compensate for the future flow loss induced by the inline diffusor? Or would the loss be so minimal as to not be an issue? I realise this question is completely arbitrary and relies on many variables, so a general idea response will suffice.

Cheers in advance.