The one thing I like about the GEO is that you can drain down the water level when refilling the Kalk. Also, you do not have to take the entire lid off as there is a smaller cap that unscrews. BulkReefSupply.com sells the Calcium Hydroxide.
My Reef System: 215g Brick 72x24x29 Dual Overflows | 4x 250w MH | 4x IceCap 39w T5 w/ Actinics | MSX-250 Skimmer | 1/3hp Chiller | 16w UV | Aquacontroller 3 | Lunar Sim | AquaSurf |Tunze Wavebox | 2x Tunze Stream 6101 | MRC Dual Nano Calcium Reactor | GEO Kalk Reactor | Pan World 150PS Pump | Phosban & Carbon Reactors