Ponds and Water Gardens - Do it yourself filter?

I have two lawn ponds.180 and 220.I have been working on them for 5-7 years.Right now the ponds are on the eastside of my house in the direct sunlight.the filtwers are on the pumps they are a foam about 8 in longand 3 in wide.The filter need changed twice a day sometimesThe algey on the bottom and side doesn't seem that bad.I have river rock ibn the bottom and it is only about half covered.My wife (knows more than I do (about this) uses a bag 2 inx 8 in with barley straw.The barley straw really helps.She has a plant in each pond.She has koi and gold fish.Maybe a fish that eats algy that is compadible . I thought if I used an external filter( home made money is the object it don't take long to spend a lot) any ideas?Thanks Ken

Most "bio-filters" today are simply tubs full of filter media. The water enters the bottom, flows up through the media and out the top. You can make one from any tough tub. You've just got to get a pump to pull the water from the pond, fill the tub with lava rock, give it an overflow back into the pond. That's it. Cheap, simple, effective, ugly! But it'll work. Just go to any supplier's website and look at their "waterfall filter" section for the basics. You could even put this right in the pond. It will work well, but be HEAVY come clean-out time. Hope this helps!