Not all air pumps are created the same. Before buying a new air pump make sure to read and understand the specifications of your air pumps capacity at a given water depth/pressure. For example the ALITA AL-60 will put out 74L/min @1.734 psi which equals 4 feet of water depth*, while a "comparable model" will only put out 54L/min @ 1.734psi = 4 feet*.
While some pump manufacturers will only specify pump performance at 0 psi = 0 feet of water depth, it makes their pump look good on paper but doesn’t tell us anything about the performance at any depth of water. ALITA has a performance chart for all their pumps which can be found for each pump we sell here http://itechaqua.com/alita-linear-air-pumps-40-80l....
For example a known brand of “comparable air pump” to the “ALITA AL-60” puts out:
Taking this into account, always be sure to make an accurate comparison when choosing the correct air pump for your application.
*Specification is given for an open ended pipe at said water depth. Adding one or more airstones/diffusers, length of pipe, fittings, check valves etc, will all add a degree of back pressure. This has not been accounted for in this comparison chart as it will vary depending on the design and material used. Added back pressure from this does need to be accounted for when choosing the right air pump, but is beyond the scope of this short blog post.