@ih57452 Thanks for your awesome ideas! I created a simple visual mockup of how this could work. I left out the mixing air pump for simplicity's sake, but think that would be necessary to get an accurate reading. What are your thoughts?
The only thing I'm still unclear on is the water flushing:
My thinking is you could take the test tube the kit comes with, drill a hole in the bottom, and connect the hose from the pump that draws the sample. That way you could run the pump to flush the water from the previous test out the top of the tube and fill the tube for the next test without having to have something to dump the water out.
How would the water sample enter from the bottom of the tube, but leave from the top? Especially if the reagents are entering through the top of the tube as well? Also, where would it go once it left the tube? I can't put the sample back in the aquarium as this would be harmful to the fish.