Could it have something to do with the alk/Ca see-saw relationship? Let me think this through ... By reducing the effluent but maintaining the CO2 we drop the pH in the reactor (presumably). This means more dissolving of media, meaning more concentrated product/effluent, but since the rate is slower there is less overall product (calcium and carbonate ions) being introduced into the tank. So presumably you already have reasonable levels in the tank, but the effect in the tank is that calcium gets depleted so long as there is enough alk to provide for that. Both Ca and Alk drop a little, but as soon as the Ca starts to go down that tends to push the Alk up higher. Does any of this sound right to you ... (pop! Ow I think I just busted a vein in my brain
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