Igorian said:Overfeeding, as previously mentioned, is one major contributor. Have you also tried a phosphate remover?
Why don't you want a UV filter btw?
I have cut the feed down to once a day in the evening when the sun's off the pond, so I'll wait and see on that one. I'm also changing pellets which are supposed to be less algae friendly.
I'm thinking of using a product from Bionetix called Aquaclean, it's a bacteria based organic treatment which is supposed to be effective at removing nitrates, do you have a phosphate remover you could reccommend?
It's not that I don't want a UV filter because I'm anti-UV, it's purely a logistical problem. Without digging a hole there really isn't anywhere suitable for a decent-sized filter. Because of where the pond is the nearest place for a hole would be in the lawn and "the boss" just wouldn't wear it!