You should rotate your elements no more than 8-9 full rotations. THis is to protect the screen within the filter that contains the Fluoride and Arsenic Reduciton media. If you can tighten the element all the way up the stem of the Black Berkey® Element, Super Sterasyl Ceramic Element, or Berkey Earth® Element without reaching the full 8-9 rotations, that is okay.
The most important thing is that you do not overtighten the elements. Over tightening can damage an internal screen inside the element that prevents media from leaking.