Frabill oxygenation packet I saw this thumbing through a BPS catalouge the other night. Looks kind of interesting and a cheap option for small systems perhaps?
I was thinking that maybe something like that might fit in a battery-operated automatic feeder. It could drop a new one in every 9 hours (that's how long the link says it lasts). Not sure how big it is, though. Might not fit, but might be worth a look-see.