I’ve been looking at ways to prevent a repeat of the algae bloom crisis. The primary reason the shrimp died was because the dissolved oxygen level spiked lower. I knew that the DO (dissolved oxygen) level was right at the published minimum level for sustaining the shrimp, but didn’t account for sudden shifts. My system is powered by a solar power bank, so I needed to be careful of the power demand. I was using a submersible pump to provide water to the biofilter. It drew 15 watts and was within the overall power draw I used to calculate my solar power requirements ( see http://backyardshrimping.com/equipment/e_solar.html). But it did not directly contribute to the oxygen exchange.
After some research, I found that many aquaponics folk are going to using airlift pumps to circulate the water in their systems, while improving the DO for their fish. The airlift pump was designed by a German engineer. Here is a general diagram of a typical airlift pump:
At the bottom of the airlift tube are several holes that are drilled through one wall of the tube. These holes are encased in a sealed air intake collar. When air is pumped through the collar, it is forced into the holes in the open-ended airlift tube to form bubbles. As the bubbles rise, water is carried up and out of the airlift tube.
There are two advantages for using an airlift pump for our purposes. While the water is pumped to the biofilter, the water is aerated and will eventually return to the pool. The other advantage is that it takes significantly less energy to power an airlift pump for the same water flow. A 10 watt aquarium pump has sufficient air flow to allow the airlift pump to lift the water to the 36″ height that I need to provide water to the biofilter.