The short answer is that the Aqua Smarte is designed to trickle in chlorine slowly, so if it dropped to zero it cannot possibly catch back up. You haven't mentioned the size of your pool, but the two pounds of trichlor in a canister would only have 15 ppm of FC for a 15,000 gallon pool. Less if your pool is larger. That's not a lot if you are dealing with algae (which if you won the green pool battle with a normal shock then you likely still have algae in the water) and on top of that it is also raising your CYA level making your chlorine less effective.
The longer answer is that Aqua Smarte is an awful device. The "minerals" in it are just some extremely overpriced silver and the canisters are equally overpriced trichlor tablets.[1]
You don't want to get too much silver in your water as it can stain, and trichlor allows CYA to build up which reduces the effectiveness of chlorine and forces you to either drain water or buy other costly products to keep algae at bay.
Their claim of using less chlorine is not only bogus, but relies on the incorrect assumption that less chlorine leads to a better swimming experience. It doesn't and the worst pools you have ever experienced probably had the least chlorine in them.
That's why you need to read the ABCs of Pool Water Chemistry, there is a lot of really bad sales literature being passed off as factual data in this industry and we are all susceptible to falling for it if we don't know otherwise.
