I have a 2021 212 QBW with 80 Gallon fresh tanks. The problem I had was knowing how much water was left in the tanks. The second LED goes out when the level drops below 40-ish gallons, the first one never seems to go off, so could be anywhere between zero and 40.
The wife gets very concerned in case we run out of water and can't flush the toilet. So this is my solution:
I purchased a flow gauge so I know how much I put into the tank. This is the one I purchased, but there are plenty out there ($22)
Flow Meter
The problem was how much had I used?
After much searching, and not wanting to spend silly money, I found this device for $26.
Inline flow meter
This unit works great, but it counts down, so you have to reset it to 100 Gallons and monitor how much is used.
When I fill 'er up with fresh, I make a note of how much I added, and add that to how much was left. Now I know how much is in her I can reset the flow meter to 100 Gallons (long press of reset button, not described in the manual)
Wife is very happy now that she knows there is water for her flush.
I found much more elegant flow meter solutions, but I didn't want to spend a lot of money on the solution.
Hope this helps anyone with a similar problem.