This is why I hate seeing new vapers go for mechs. Most places don't give new vapers the info they need to use a full mech effectively and this is always the result. Blaming the tank when its actually the mod itself that is the core issue. PRotanks are not really designed with full mech mods in mind but more for the std volt range batts such as egos in the 3.0-4.8 range.
YOur pushing out about 4.7 volts on a full charge of that batt and on the mini thats too much power for a 50/50 juice on a 2.2 or lower coil. Your also probably taking 5+ sec hits and 50/50 doesn't wick fast enough in the protanks to keep the coil saturated at those voltages for more than 2-3 sec hits Step up to the 2.5 coils or get yourself a kick regulator and set it for 7 watts. Better yet put that k100 away and get yourself a good VV/VW mod like an SVD, Evic, TEsla or even just an Ego Twist so you can actually have control over your power settings and learn how to dial in the mod for the coil ohms and what the juice likes. IMO you will have a better vape experience in the long run if you step back from the full mech mods and into a good vv/vw mod so you have more control over your vape.
You will find that the protanks like a range of 3.0-4.6 volts depending on coil resistance and juice. As well as juices with base mixes of 70PG/30VG -100pg without modding the stock heads. ANything over 30% vg and you need to remove a flavor wick unless its been thinned out like some high vg juices from totally vaped out and a few others. I use protanks with very little issues and heres some of the tips I came up with based on my experiences.
http://www.e-cigarette-forum.com/forum/new-members-forum/529727-kanger-protank-tips.html