Rio pumps are great, I am running about a dozen and none have failed for any reason over the past 8 years. The 2100 will pump about 3/4 the volume of the 2500 unless the lift is over 4 feet; however the 2100 draws about 1/2 the power.
I am currently running about 25 submersible pumps and have found the Laguna (Hagen) submersible 7000 and 10000 to be the most efficient brand, among those I have tested, for the power actually used. It appears all pump manufacturers over rate their pumps; I think they test them with a slide rule and come up with a theoretical performance curve. I ran all my tests with a large volume of water and a large diameter hose using the same vertical lift for all and measured the current draw (amps) with a clamp on amp meter with two digit readout. Most pumps appear to draw more power than specified in the manuals.
Water pumps are different from air pumps with regard to current draw. An air pump / compressor draws more power as the pressure builds with a resultant reduction in the volume of air moved. As the air pressure is reduced more air is moved with less power consumption. Water pumps on the other hand draw less power as the head pressure builds with a resultant loss in flow rate; however in a low head situation where more water is pumped, more power is consumed.
If given the choice an external pump such as a Sequence or Wave and many other low head highly efficient pumps will deliver as much as twice the water flow as a submersible for the same power consumption. For example I have a nice Little Giant pond pump which draws 300 watts and delivers about 1300 gallons per hour in a particular configuration. I replaced the Little Giant with an external pond pump which draws 2.6 Amps (2.6 Amps times 120 Volts = 312 Watts); but it delivers nearly 4,000 gallons per hour. What a significant difference between external and submersible pumps.
) and it never gave me a single problem
