Yikes! that's a big font...
OK, my limited knowledge would say eeeekkks! The biofilter takes approximately six weeks to cycle. DO NOT rinse your biofilter with a hose—are you on untreated well water? Chlorine will kill your biobugs. I use a bucket to scoop up some pond water, after I have drained the water from my biofilter—using the stock BD that is in it, I then will dump the pond water into the top of the biofilter and watch the color of the water coming out the drain. After several dumps the water is much cleaner—I'm done. Close it up and turn the pump back on. If your cleaning your biofilter every couple of days it's obviously getting to much yuk. You need to dramatically improve your mechanical filtration. Did they run the bottom drain to your skimmer, or do you have an additional filter for that?
It will take time for your pond to settle in. If it's brand new, the algae isn't even helping you yet. I had minimal fish and when the pond was cycling for the first time it started to get so green I could almost not see the bottom then bang it went away. I wasn't feeding the fish and I only had mosquito fish at the time. I've read conflicting views on water changes and new ponds but given the food and fish number you should probably be doing some of that—again I'm no expert and don't know koi but the folks at koiphen or koishack will be much more informative—even if all you do is search the old threads.
Your pump is costing you a lot of $$$ to run. Even without knowing at what head height your pump does 4200 gph at. A 1/2 hp pump takes a lot of juice to run. A 1/6 hp pump @221 watts/2.3 amps will push 4000 gph @ 3.5' head for comparable flow.
32 1" koi or 32 8" koi? There is a formula for number of inches of fish per 100's of gallons I don't know what it is—the koi folks at koiphen could tell you. Given you have koi I am guessing you are WAY under filtratrated. I've heard one koi for a thousand gallons—the local garden center here says 1 koi for 10 gallons so opinions differ immensely, but the folks at koiphen can guide you better than I. Also 3–4' is a minimum for koi.
You have about two hands full of glop per day coming out of your fish, not to mention the snails contribution—mine came uninvited with my new plants.
"The twigs or" is why I added brushes soon after building my pond. Your telling me you have one little mat for mechanical filtration for 32 koi? You have a roll of springflow and one scrawny mat for biofiltration... that's it? I don't expect the lava rock would help you for very long if you were to do that. You need to begin with a great deal more mechanical filtration IMHO.
The plastic screen in front of my skimmer is the old plastic rain gutter gaurd stuff they used to sell to keep debris from clogging up gutters. I have two of them. The bottom of my pond comes up to just below the front of my skimmer faceplate so one sits on the bottom the other rests on top of it and the water current helps hold them in place. Mine is essentially for catching all the algae that is constantly floating around.
14" Brushes in Savio:
http://www.aquaticpondsupplies.com/brushes.htmMatala I used a roll of blue:
http://www.matalausa.com/Extra Mat I got from a "local" koi shop—same stuff that comes in the Savio when new.
Instead of Matala you could use:
http://www.bettymills.com/shop/product/view/Premier/PAD235.htmlor
http://www.shoplet.com/office/db/gFPAD1199.htmlI can't tell you what color floor scrubber pads or size to get, I've never used them.
Here's a link to DIY filters at koiphen—you'll need to join to see pictures... also read through some of the construction threads
http://www.koiphen.com/forums/showthread.php?t=51710 There's a section on bottom drains too, in that link.
Another great resource is a guy called gene at
http://www.koivillage.com/ he also posts at koiphen...