Update, it seems that evaporation in the sump has slowed considerably. The "boiling" caused by the commercial air pump lead to a rapid drop in water level in the sump.
The other issue I'm having is fine detritus powder is coating the bottom of the tank. A wavemaker was delivered yesterday. I'm going to add it to the non-overflow side of the tank near the bottom of the water column. The aim is to create a circular flow that will carry water from the returns, to the far end of the tank then, back to the other end along the bottom, carrying the detritus to the canister filter.
If I can perfect this flow, my upkeep will be minimal on this tank. The K1 is self cleaning. I can disassemble and clean the fx4 every 4-6 months. And water changes are a breeze since the tank is drilled and plumbed allowing me to drain 40% with the twist of a ball valve. No gravel to vac and refills with a garden hose.