You have a leak.
Pressure it back up and soap test, (dish soap and water) all of the connections you can see/reach and watch for bubbles to grow. Or call your local LP dealer and see if they can do it for you. Could be a loose connection, could be a leaky hose or pigtail.
PS the green shows if there is more than 10 psi between the tank and the regulator, less than 10 and the regulator will switch to the reserve tank.
Jim & Debbie England
Do you have Gas? 2015 F350 6.2L CCLB DRW 4.30 axle. 2012 Yellowstone Ridgeline 34RLT Fifth Wheel