I am fairly new to ponds and fish keeping. My step father and I built our pond two summers ago and last summer it started leaking and we were unable to find the leak. This spring or summer we are planning on completely redoing our pond and try and do a better job of making a filter. We plan to put in a bottom drain at about 3 feet and we plan to have about 1500 gallons total in the pond. We have a pre-filter box with some filter media to keep leaves and bigger stuff from clogging the pump. I have been watching a lot of videos on DIY biofilters and would like to know how big of a bio filter we would need to make for this size of a pond with around 8 goldfish and 3 koi. (i do not need my water to be extremely clean or anything i just want it to be better than it was last year when we couldnt see 1 foot down for most of the summer) My original thought was to make two filters from big flower pots and position them above where i want the waterfall and then have them run into the waterfall pond before going into the big pond. Any advice I can get would be greatly appreciated. Thank you very much.[/quote]

hi there
you will be looking at 2x 55 gallon barrels or waterbutts for a 1500 gal pond minimum with you having koi althought you only have 3 koi they produce twice as much waste as your gold fish
if you use two/ three or even four of these barrels/waterbutts then you can create yourself a pretty good filter the more media you have getting finer in each barrel the better it will be.
for an idea of what to use, use the first barrel as a vortex with vortex brush this will catch the large waste,second with bruses this will catch anything the vortex didnt,third fill with jap mat catches the finer stuff and the fourth with flocur this is your main bio with a layer of jap mat to help stop the flocur flowing out you can also have a layer of filter wool in this bay as it wil catch thevery fine stuff.
the fines are what cloud your water
also if you have a tea colouring to the water this is docs caused by decaying food, vegitation and high protien foods

you dont not say if you have a uv in line this will help with any free flowing algea this is what makes your water have a green tinge or the look of pea soup

try to keep your old filter going while you build your new one then transfer the old filter media into the new filter this will cycle your new filter this will help reduce the new pond problem that can occur with new filters
cylcleing can take from 8weeks to 3 months to fully become mature
always clean your filter media in pond water never tap water this will kill the filters and you will have to cycle all over again

hope this helps

saph