have you read on here about the RAS systems, and how hard do you think it would be to customize one to your situation?? Its a thought,... it may take a building for the RAS to sit in so that the algea doesnt over come it, but the cloth buildings are getting cheapper every year??

So how long would it take to cycle 250,000 gallons??

would a complete filtration of your pond in a week do the trick for you?? of course there will be limits. Have you considered dying the water blue??

is there lots of muck on the botom?? If you drained and cleaned it out and put in defusers or a surface fountain??

If your budget is Thousands a year, hire an expert to come take a look, and see how close he thinks you could get to your goal.!

Water is the basis of all life, by design!