If I'm not mistaken, the sugar idea originated with the old Orchid Wrangler, once an importer of a lot of plants that typically came in rootless.
Todd Zimmerman, who is an educator in the field, told me he feels it's a waste, and that pure water is probably the most advantageous soaking solution - maybe with rooting hormone, if you're so inclined.
Back to Scott's comments, for a moment: I believe it is NOT a good idea to wait until the reservoir is nearly empty before watering, and as he has found out, watering more frequently is actually a very good practice.
Between non-uniform nutrient absorption by the plant, evaporation, and the effects of plants' respiratory processes and gas exchange at the roots, the solution in the reservoir can end up a long way from where it was when you watered.
Waiting a long time between waterings lets the plant "sit in its own wastes". Topping up the reservoir only dilutes those wastes, but the quick-fill-and-let-drain watering technique probably is the most effective at eliminating them.
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