@_Steve posted:I like this idea. Nicely done. This is probably now on my list.
One more thing you may want to try out in the calibrating step... I noticed, when I was calibrating my "sight-glass" mod, is that my tank had several unusable gallons at the bottom. Three I think. I don't know if that is a normal condition or not. I figured that out, when after draining the tank completely and de-priming the water pump, the pump would not re-prime until there were 3 gallons in the tank. I did not test the other direction ... in other words, if the pump was still primed, would it pick up the last three gallons? In your set up, it might be an easy thing to test ... when Mopika says there are only 5 gallons left, turn on the pump and see if how many it says are left when the water stops flowing. Just a though.
Side note: The "sight-glass" still works and is way better than the indicator light for that bottom 1/3rd. But, it isn't very good when you get down to the last 5ish gallons... and it is kind of a PITA to keep clean. I think I may give Mopika a try.
I was very tempted to do your sight glass mod. I never moved on it because I had a pretty good 'windage' guesstimate by knowing how many gallons I started out with. Then I saw the Mopeka water tank gizmo!
The gauge doesn't seem to be able to gauge the last ~5 gallons in the tank. It re with poor quality signal. Perhaps that is because I have it mounted on what appeared to me to be a slope in the tank near the water pickup. Maybe that's where the hidden 3 gallons you describe is, in that little well.
I'm not certain there is a well/low spot there. The slope makes me think there is at least in my tanks installation. In all the assembly line pictures I've seen it looks like the tanks are uniform. Perhaps that PVC pipe running towards the drain pushes up on the bottom of the tank physically slightly deforming it and forming the well as a result.
