I've been using the crown
tank for a couple months now, and I have had a few instances when the top would be "stuck" on there and I can't seem to get it off. Generally this happens after many refills and I think I might just tighten it too much... although as you said I try to screw it on not so tight.
Generally what I do is take the
tank off the mod, then use something grippy (like the stuff you can put down in cabinets) or I'll take a allen wrench and put it in the air flow hole to hold the tank and then unscrew the top.
I have had a couple of times when neither of those worked... I waited till the tank was just about empty then I'd take it apart and then grip the inside of the top (where you fill it) with pliers and then screw the top off of it.
Annoying yes... but I have to say I really like the vape I get off this tank and I don't have to rebuild anymore. The other nice part is I can vape about 100ml of liquid before I need to change the coil. So.. for me that's pretty good.. 3-4 weeks or so.