and with those crystals you could make cool looking gel/gravel combo where the gravel looks like it's suspended in mid air
you can, but as i mentioned before over the period of a week or two algae starts to grow on the exposed gel "crystals", not only on the surface, but it also penetrates into the gel as well; basically turning all the translucent "crystals" green.
i suppose some for of algacide could be added to the water on occasion to supress the growth ... not sure how practical this is though.
Water retentive polymers are used with mixed sucess through the middle east (even some open air examples - such as turf areas) to reduce water consumption, as well as loss of water through evaporation and gravity (particularly in sandy soils). One of the drawbacks of the prolonged use of these products in arid areas is the apparent absorption and buildup of salts within these gels - which obvioulsy have a phytotoxic effect