I am quite new to pond keeping and over here in Cyprus theres no real outlets for professional supplies etc so its hard to source equipment.

We have a shaped pond outside with normal liner ringed by stones. It is serviced (last year and this) by 3 pumps each with a home mead filter going onto a larger bio type filter then by gravity back into the pond.

Previously the water has been absolutely crystal clear and the fish and lilies loved it.

However this year we inherited some more fish from another property where the water was black like soup and you couldn't see 2 inches under the surface.

Since introducing the fish my water has gone thick green, I am changing/cleaning the filters every second day because they get so clogged up with gunge.

I have used 2 loads of Algizin in the water (all my pet shop had) and theres no improvement, if anything even worse.

I live at 500meters altitude, winter it is outside only 4 degrees and summer can hit 50 centigrade, the water has never frozen.

What should me next move be to try to clear the water please.

Thanks in advance.