Thanks for the comments. From what I have been able to find out, using water crystals as a soil-less medium has been successfully tried (with evidently outstanding results) on several kinds of household plants, such as lucky bamboo, ivy, and peace lilies. It's not recommended for succulents (which cannabis is not) or for plants that need direct sunlight. This last is because the polymer crystals begin to break down when exposed to UV light. However, I plan on having the medium completely sealed from light (as in a bubble bucket) so this won't be a problem.

As for the oxygen issue, it seems from literature that I've been able to find, that the water absorbed in the crystals retains it's oxygen and nutrients until transpired by root filaments which penetrate the gel membrane. Standing crystals don't stagnate and lose infused oxygen like standing water does (at least that's the claim). One piece of literature even specifically mentioned using water crystals for plants which are usually grown hydroponically (is that a word?)

So, I'm going to take their word for it and not use an aerator. I would like to do 3 simultaneous tests. One in a "standard" soil setup, one with the same soil but with water crystals added as a supplement, and one with water crystals only (quasi-hydroponic). Well see how it goes from there.