You say "pro Air" so I assume itís a 1999-2000ish model with the old aerator pumps. I donít have that exact boat, but my 2003 shouldnít be too far off.
Your first problem is that the gauges are not reading and IMO you donít need them with this type of ballast system anyway. The problem is probably a sending unit issue. Remove the sending rod from the top of the tank, slide the float to make sure its not registering and replace. I only had one go out so I was able to swap a sending unit from another tank to make sure it wasnít the gauge or wiring that was broke.
It sounds like your second issue is that one tank is not draining properly. There should be a pump to fill and a pump to drain for each tank. Check the drain hose and pump for the tank that is not draining. Make sure there is no clogging debris or kinks in the hose. Check the pump and if itís not running, test the power or replace it.
Sending units and aerator pumps are not that expensive. Replacing them with bags is your call (you will get more weight with bags), but you will still need to buy at least one aerator pump and still will not have working gauges. You will also need more weight up front if you slam the back with large bags.
Check out planetnautique for more detailed information.