Yes, that is a very high bubble rate. It certainly wouldn't be acceptable to me, but if you don't mind the re-filling so be it.
I would use some soapy water and check all the connections from tank for leaks. If you don't find any I'll be surprised, but not too surprised as many people have this kind of issue with wet-drys.
It's hard to estimate the flow rate on an individual CO2 tank, but I would not be surprised if you have to re-fill in a month or two. Maybe sooner.
Keep an eye on your regulator. When the gage starts to drop, it's running low. It should say 850lbs/sq in. when full. When it drops to 600lbs. get it filled. When mine gets that low I have a pound or less in the tank. Letting it get lower, for me risks a gas discharge into the tank that could kill fish.
If I had a cannister filter around I'd use it in place of the present one. With a kH of 6 and a cannister, I'd estimate your bubble rate for the same affect would be about 2 - 4 bps. That, of-course assumes you have no leaks in the CO2 system.
Len