I'm assuming the tank is a Herakles, not a Herkules, but please correct me if I got that wrong
You didn't mention you were getting obviously burnt hits so I am assuming that was not happening. I would still try a different coil head just to make sure there is nothing wrong with the one you're using.
If it was actually firing at 30 watts the Herakles was at the low end of its power range, but you could try lowering the watts and see what happens. You can't go too low, if you like the vape it's all good so try it and see.
The Halo Triton with the tank they come with is probably running at around 8 watts. If you like that vape there is no reason to use something that requires more watts and you have a few choices.
You could get a
eGo to 510 adapter that screws on the Sigelei and use that to mount the Triton tank on the Sigelei. The Sigelei does 5 watts at the low end so it will be fine power wise. Your battery will also last a long time on a charge at 8 watts.
You could get a tank that runs at that power level and has a 510 connection built in like
a Vision Vivi Nova or a host of similar tanks and use that on the Sigelei.
You could sell the Sigelei in the classifieds here and buy a less expensive, lower power mod like
an iStick 20 watt for $30. That one actually comes with a eGo-510 adapter. It also has a built in battery.
Good luck with it.