when I use my subtank with my xpro the ohms will jump as high as 3.0 and drop as low as .2. this is due to the tank shifting back and forth on the 510 connection. it does not happen with my aspire tank and I'm guessing this is because the tanks connector is shorter. to solve the problem I put the extra gasket that the sub tank comes with between the mod and the tank. it's a temporary fix and hopefully smok will come out with a better spring loaded connector.