Put tank 2 into the tank 1 position to ensure that it's functioning properly. If it is, it sounds like the switchover regulator may have a problem. I had one go bad on a trip, and had to replace it... fortunately, I found a reasonaby priced RV dealer within 20 miles, as the CG that we were staying at had a regulator, that they wanted WAY too much money for the convenience....
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter