chileguy, that aspect was actually brought up by Rovert on page 3 in his 06/07/2007 11:41 AM post. It's a point I've considered as well. An analogy can be taken from gardening, where applying a basic fertilizer having appropriate macronutrient ratios of nitrogen, phosphorus, and potassium would be the equivalent of dosing 2-part. But with plants there are other important nutrients (Fe, Cu, Bo, Mg, Co, Ca, etc.) that are also necessary, and I've wondered if there are reefkeeping equivalents of those that are dissolved and dosed by Ca reactor media but are not present in 2-part dosing. The answer here has been "those micronutrients are replenished by water changes", which may be true, but then in that case it takes away from the idea of a 'stable tank', and the micronutrients are doing a boom and bust thing instead of being kept constant. I would think a Ca reactor may help keep micronutrients at a more constant level...