Question
my pond is 20ft long,13 foot wide and 5 foot deep, i have mixed fish, approx 25 in total, mainly koi upto 12 inches, goldfish, and 1 mirror carp about 6 lb. pump is about 15000 litres, 3 lily plants (about 12 lilly pad leafs) and 2 other plants. the pond is very green algea,this is my plan to cure do you agree or can youi give any other advice.   drain 18 inches of water, clean algea of of liner, hoover any sludge from bottom of pond, clean as much weed as poss, clean filter add pond clear and replace water level. many thanks.

Answer
Your cleaning program should help.  You'll have to be careful while removing sludge to not stir things up too much and release bad gases in there.  Do you have a Pondovac or some other pond vacuum?  The water change and physical removal of the algae will not control it long term.  Removing the sludge will help though.  For tips on controlling green water, see my pond algae page at http://www.fishpondinfo.com/plants/algae2.htm
I saw your question as I was going out the door at work yesterday but I was in a bad mood and exhausted so I waited until today to answer after doing my 12 hours of chores so that I could hopefully give a better answer!  You have a nice big pond but cleaning it is no easy task especially 5 feet deep!  Good luck!

Robyn