Leaking Tank Valves

I purchased 6 new Catalina AL80 tanks with Pro Valves about a year ago for my family to dive together. I had the tanks inspected, the valves installed, and filled at my LDS. We have been using them with no problems, however, tonight I noticed that 4 of the tanks have very slight leaks where the valves screw into the tanks. I checked the tank pressures and it seems like the worst of the leaking tanks might be losing about 100 pounds of air per month. My first question is whether or not it is normal to have slight leaks? I took a wrench and tightened one of the valves about an eighth of a turn and the leak got worst. I loosened the valve again and the leak almost stopped. I will have that tank serviced tomorrow at my LDS.
My next question is what to do now? I will bring all of the tanks to my LDS this week. Should I expect to have to change all of my O rings or will I need to change all of the valves? I would appreciate any advice and recommendations.

My guess is they overtightened the valves and/or used lube on the static neck O-rings. Be very careful using a wrench on valves when pressurized unless you know what you're doing. Very easy to damage soft brass. If you have a whip, drain one tank, remove the valve, replace the o-ring (size 214) and hand tighten plus 1/4. Then transfill from another tank into the empty. Drain tank #2 and repeat until they're all done. Then bring them all back to the shop to get topped off. No reason to pay the shop for anything but a few O-rings.

You've had them for about a year? They are do for inspection anyway. Don't tighten valves with pressure on the tank. You could blow up.

Thank you so much. I am especially glad that you made me aware of the "blowing myself up thing". I guess I didn't give enough thought to the amount of pressure I'm dealing with. I'll bring all of the tanks to my LDS this week for new O rings, inspections, and air fills. Thanks again, your assistance is greatly appreciated.