240mg/L KH reading. How do I adjust down?
possible reason for this hike?

Not sure what that reading is myself what test kit are you using?

Normally kh is measured between 0.0 - 16.0, If you are using Bio-calcium on a tank that contains no hard corals then it will rise rapidly and shouldnt be used as you may run into trouble if you dose too much.

As a bench mark 9 should be what you be aiming for give or take 1 or 2

Or is the reading this on salifert Alkalinity in meq/L 2.40 which means you have a reading oh 6.7 on kh which is too low?