I was working on a drop checker yesterday for a friend's Fluval Edge, and I started thinking to myself, "How could I take advantage of the unique design of the Edge?" I realized I could make it readable from above, through the clear top of the tank. Additionally, a drop checker is mostly full of air, so it should just float against the glass, no suction cups needed. I came up with the following:
It is just over 1" diameter and 1/2" thick including the 1/8" clear acrylic top. Unfortunately the plastic I had is a bit yellowish, and may skew the color of the drop checker solution a bit. I tried two others using Teflon because it's whiter, but of course I couldn't get any of my glue to stick to the Teflon.
The surface area of the water in the lower section is pi*.447^2=.628 sq inches and the surface area of the test solution is the same minus the area of the riser tube .628-(pi*.125^2)=.579 sq inches. Hopefully this will be enough surface area to get a decently quick reaction time.
Initial tests show that it does float when filled with an appropriate amount of water, but the surface tension in the upper chamber pulls the liquid to the edges, so I may need to make another prototype with a deeper chamber.