 Foaming sludge in filter
HI there just wondering if anyone can help me , i noticed in my filters about 6 weeks ago alot of dirty foam forming and then also in the pond itself i thought nothing of this as the pond is 2000 gallons and has 2 nexus filters and a foam filter with 2 large air pumps which is more than enough for the pond size , i have now lost about 5 fish but dont know why this should have happend i have changed half the pond water i think the water has released all of its undissolved organic compounds any ideas thanks | 
