brownish water

hi i got a 2900 gallon pond made out of an old pool liner and for 2 years have been doing everything i could under the sun to get it up and going. i got a 3000gph pump with a bucket filter using quilt batting, ive use alot of the store bought bacteria and i control the agle with aglicide but the water just stay brown or brownish.i got 3 koi and 7 goldfish that started as feeders and are about all 3 inch now.the nitrate and nitrite are at zero its soft water,the alkalinity is 80 or moderate and my ph is 7.2 so all of it is fine ive tried the chemicals that bind the particles and all that stuff plz help if u can.