There are several different types of water pumps used for many different applications of moving liquids in various forms i.e.
Centrifugal
Diaphragm
Piston
Reciprocating
Rotary Vane
Axial-flow
Plunger
Rope
Screw
Hammer
Lobe
Displacement
Air
Rotodynamic
Peristaltic
Progressive cavity
It would be great for the community to share what type of pumps they are using on their AP systems including make, model, maintenance problems and functions etc…
Note:
Not many people have taken into account when purchasing a pump, what impact it would have on their fish in the form of underwater acoustics.
Most of us have already experienced numerous types of unnatural acoustics from our alarm clocks, burglar alarms, traffic noise etc…
With the constant hum from pumps and other machinery in an AP system, fish can get quite stressed out like us humans in the same environment.
There are pumps on the market that produce a noise level lower than 23dB but are not practical in AP systems but a general rule of thumb aim for something around 50dB.
For those who already have existing pumps in place, I found that adding a high density rubber mat or foam under my pumps worked very well.
Why we should be concerned about underwater acoustics?
There are countless publications on the topic online that can explain in more detail for example:
https://asa.scitation.org/doi/10.1121/1.402200
I have personally found in making informed decisions and adjusting my previous systems, has reduced fish stock loss and oddly increased fish body mass due to changes in feeding habits.