Tried .5 -.7 Rba builds and .5 and 1 ohm occ coil heads just to strong for me . So I put an extra rubber top seal on my protank coil heads and it works Awesome lots of smoke good flavor no leaks.will try working my way up slowly not sure if you can use protank 3 heads or not . Just Thought you guys my like to know this! ( oh make sure you turn the watts down a bit)