I'm close to selling my koi flock and landscaping-over my pond. I'm a prisoner to my pond because I have to backwash my biofilter every 24-36 hours. It's worse than having little kids around. Can anyone provide some guidance on how to proceed other than by putting my control valve in "exhaust" and calling it a day?
My 1200 gallon pond is 20 years old, EPDM liner, UV, and I'm using an Aquadyne 0.60B with the air blower (now called model 2000). I don't have a bottom drain. I'm using a Matala aeration system and the biofilter exhausts into a small waterfall (via the UV). I haven't had gin-clear water in years. Before the bio installation that was understandable and for the 2-4 years after I installed it in 2010 everything was fine. But for the past few years, after bringing the biofilter back online after the winter (I live in Annapolis, MD) things have not gone well. From this April I've had maybe 2-3 days of clear water and maybe 10-20 days of an acceptable, slight green tint. Otherwise, I've had to deal with foggy green water and also with suspended algae that grows on the walls only to be disturbed by the fish and forced into solution. I add bead filter bacteria after almost every backwash. I have a pond vac, which I've used 3 times this season so I keep the bottom pretty clean of leaf debris. Ammonia, nitrite, and nitrate levels are good as is phosphate. Ph is 7.2. I was adding liquid barley extract until I was confident that the pond was free of leaf and twig matter.
Fish load: 10 koi. Average length is about 16 inches. The three largest are a good 20-24 inches.
When I backwash the biofilter, which is indicated by a slow waterfall, the effluent is as dark as squid ink. Very dark, opaque green. Nearly black. My perception is that it's mostly "fines" as the visible algae debris doesn't appear to be excessive. It takes 2-4 backwash/rinse cycles to clear the filter, which buys me another day, maybe two days if I'm lucky. If I get lazy and let it go 3 days without a backwash the waterfall will slow to a trickle. Oh, and I use the blower 2-3 times per month, not for every backwash.
In closing, in desperation I put the **** thing on bypass this morning to see if perhaps the higher circulation will help. But I'm hoping that the learned folks on this forum have some ideas that I can pursue.
Thanks for reading this far!
Frank Mackowick, Annapolis MD