dart pump question

[hillegom]

From the Reef Aquarium, by delbeek and Sprung vol 3 2005
Page 111 table 3.4
For every 1.5 in 90 deg elbow The extra resistance in thermoplastic pipe in feet is like adding 4 extra feet of pipe.
Let me restate
Adding a 90 deg elbow into 1.5 in pipe increases the resistance of the water as if you added 4 more feet of pipe.
How much resistance equivalent to feet of head, depends on the volume or g/hr you are pushing with the pump