Hi quest01, if you have measured the flow rate accurately, here are some numbers. A horsepower is equal to raising or lowering about 33,000 lbs. a ft. per minute. 30 gallons weighs about 250 lbs. X 6 ft.drop or 1500 lbs. per minute. Divide that by 33000 lbs and you're rough potential is 4.5 percent of a horsepower. 33.9 watts potential ( although it's 24/7 unlike solar panels)Then you must figure in losses... If you haven't measured with a bucket, or some other means, you could be way off. It doesn't take much time to do... Good luck, hope something made sence... If my numbers are incorrect hopefully someone will catch it!
As for a pma being able to convert the power, it can be done. Otherpower (top of page ) has lots of experiments... can even capture the power of a hamster (Skippy weighs a lot less) ...Gary D.