I used to use the 4 liter ice cream containers for baby brislenose and young chiclids. Also used 2 liters with an undergravel filter.
The big plastic bottles are ideal brine shrimp hatcheries. Real easy to clean, just place in recycle bin.
I'd be interested in any photos if possible.
One thing about air stones, I found that if I used a marlin spike (on a swiss army knife) to make a hole for the airline near the rim of the bottle, then that would hold the air stone in place.