A water pump is the primary life source for an Aquaponics system. This decision deserves attention and research. A bad choice can keep you purchasing new pumps every few months or not delivering enough water turnover for your fish.
There is a comprehensive water pump flow rate generator that will get you half way there by calculating the liters/gallons per hour needed. You only need to know how many Media Beds and DWC taps you have in your system, and how much water is in your fish tank. The next decision is quality, type, brand, and submersible, in-line or air.
Maintaining a pump is a part of farm maintenance. It should be assumed that you'll need to clean your pump at some point. When you have an in-line pump you'll encounter less blockage than a submersible pump. This is because submersibles are directly in the water collecting much of the waste and algae buildup.
If you purchase a random brand, there may be a good chance the parts won't be available when you need to repair something that gets broken. Consider a more reputable brand as they will have better support and return policies.
Any aquaponics system should have some form of a backup system in place. This is especially true in commerical systems. When a pump failure happens you need to have a backup on site to replace it. If you're in commercial aquaponics, you should have a pump inline so you can do a quick switch without needing to rewire it. Purchase a pump that you can afford to purchase two or more.
Pumps always have a chart related to how much a pump can lift water. The maximum head is the height a pump can push to before the flow rate goes to 0.
What we're trying to do is find a pump that can handle the height we need to account for while maintaining the flow needed to circulate our system properly.
Let's say our calculator calculated we need 4,700 lph. We would look at the chart provided by the manufacturer on head. It would look something like this:
In this example we can see that our 4,700 lph pump can deliver water at that rate up to 8 or 9 meters.
Maybe you have a home system and only need to raise the water 1 meter. That means that you could deliver almost 12,000 liters per hour. That is significantly more powerful than needed.
If you're looking for a decent pump, take some time and weigh the different pros and cons. If you're just starting out and this is all too stressful, the Active Aqua Submersible is a good starting point for a home system. For a commercial system you'll definitely want a more industrial pump like those you can find at Grundfos.