Interesting concept of larger bubbles maintaining a larger ice free area. Larger bubbles will create more 'apparent' activity at the surface. I'd like to see results from a test of the two diffuser styles. My logic concludes that you will get a larger ice free area from the diffuser that produces the most water flow, which is what is deterring the ice formation; flow or current. The farther the current spreads the larger the ice free area becomes assuming a constant temperature.

Larger bubbles seem to make more activity at the surface but the current or volume flow across & under the surface will be less than with finer or smaller bubbles.
Try the hose only this year and save your money to buy a membrane or stone diffuser next year and compare. Let us know your results. 0.75 cfm will run only one 6" airstone. You will get better results from an 8-10" dia membrane disk. Stones have to be cleaned in acid whereas edpm or rubber membranes can be scrubbed with a brush or scouring pad & water.

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