The runoff from agriculture that causes those algae blooms you spoke of has a lot more phosphorus than you're azomite will add, unless you put too much in the jugs. You can grow algae well in 50 ppm of phosphoric acid. If you don't have rock phosphate handy, try any nutrient that is high in phosphorus and add a smidge.

I like the soda water idea. If you have an aquarium air pump handy, you may try that in a jug. Bubbling air and with enough phosphorus you could probably get a pound out of a jug. You're right, they need as much CO2 as they can get. The water will exchange enough with the air to grow quite a bit of algae, but you can get more if you can supplement it.

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