Bag test...Bahahahahaha. If it was me writing the response, I would omit the bag testing. Makes the company look like amateurs. I guess you can use a fast frame camera and volume to do some calculations, but wouldn't that be more expensive than the method used by Jake? I can't rip them using theoretical math, I'm sure most companies also use it. No real way to find out except to know all the companies method of testing.
Idea for next years science fair: How flow is affected in an aquarium. Test flow at different distances/depths from the powerhead, obstacles, shape of tank, dimensions of tank, position of powerhead. You can get into desired effects, but that can also be a separate experiment for the following year using the info gathered in the first test.
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