Let me first say...
WELCOME!!!
Quick disclaimer: I don't have first hand experience with bead filters, but I've done quite a bit of research. I am going to get a bit windy here...
From looking at a description of the Aquadyne line, at
MacArthur Watergardens website, looks like you would be going for the 2.2 model for a recommend 5,000 gallon pond which requires, according to their
operation instructions, a 5,000gph pump to properly backwash the unit. You could go for the 1.1 model for a recommended 3,000 gallon pond that only requires 3,900gph pump. only
IF you were to go by your pond's gallons recommendation.
The bead filtration unit is a combination unit. They do both mechanical and bio-filtration and this is why it must be backwashed. Backwashing simply stirs up the special beads inside the unit so the beads "release" the debris and the debris gets flushed. I am told this does not disturb the bacteria colonies, but this sounds odd since bacteria can be disturbed by water shear so I'm gonna reserve my skeptism about the "backwashing not disturbing the bacteria" for now.
You
must use the correct pump, the flowrate recommended by the manufacturer, to properly backwash the unit. If you ignore to maintain frequent backwashes or the backwashes are too weak, then the beads will not be cleaned of debris causing the unit to not perform efficiently.
You need to not trust the manufacturers on certain things. I know it is a wierd thing to say. The problem is matching bio-filtration units to "recommended pond volumes". Bio-filtration does not care one bit at all about how many gallons of water your pond has. Bio-filtration only cares about the naturally occuring bacteria, housed inside the unit, processing dangerous ammonia into "safer" nitrates, which is all part of the nitrification cycle. Your fish, plant decomposition, and even fish food eventually creates the bad stuff that the bio-filtration feeds on to make it "safer". "safer" in quotes since the end product, nitrates, can be harmful to fish eventually in very huge quantities. The gallons of water has absolutely zero relevance to volume of bio-mass to be processed by the bacteria. Bio-filtration must be matched, or slighter bigger, than the actual volume of daily biological waste produced inside your pond. This can be extremely tough to do, at best is good guessing, so most manufacturers simply say "recommonded pond volumes".
However, the Aquadyne actually gives you a "total pounds of fish" recommendation, which is much better to use rather than pond gallons. USE THIS instead of the "pond volume recommendation". Since the Aquadyn does takes this extra step, then this makes me feel a little bit better about the product. For bead filters, I'm a bigger fan of the
Advantage bead filter setup due to how it is setup and it has options; unfortunately, it costs twice as much as the Aquadyne. I have always read, when going the bead filter route,
always choose the filter system that is 2~3 times bigger than your fish load, but you can go with any of the units to see how long it lasts you. Generally, if you are able to test any ammonia or nitrites at all, then this means your bio-filtration unit is failing and it needs to be improved or expanded.
"9 large koi and 3 goldfish". I generally assume each koi is 17" koi and golfish 8"
if not fed much. I also double the inches of koi since koi produce much more waste than an equivalent sized goldfish. If you do take care of them with many frequent, high quality feedings, then I would assume each koi might get up to 32", then double that for my calculations, and 12" on the regular gold fish. With my calculations, you have .8" of fish per 10 gallons at least, or 1.7" of fish per 10 gallons of water at most. You'd probably be fine with some sort of cheap bio-filtration unit that you can DIY very easily so I would think just one bead filter, that equally matches your total pounds of fish, would be enough for your pond. HOWEVER, the fish do breed so you might have to take into consideration of the new koi/goldfish if you can't do some population control or can't give them away.
Koi Weight. Koi weight all depends on if they are a standard fin (which is your typical koi) or a long fin (which is butterfly koi). A 16" koi is approximately 890grams (that is 2 pounds) and a 24" koi is approximately 3,050grams (around 7 pounds). A 32" koi is approximately 9,008 grams (around 15 pounds).
I'm not for sure how much the regular, comet goldfish, would weight, which is probably not much at all. I would probably be generous in saying a 8" comet gold fish is half a pound.
If your "9 large koi" that were 16" each and your gold fish 8", then your total fish pounds would probably be around 19.5 pounds. If you were doing high frequent, high quality feedings, then probably be around 139 pounds total of fish.
So, best to choose your the size of your bead bio-filtration unit according to the total pounds you think you might have in a few years, which could be 19.5 pounds or 139 pounds.
You could take the easy route, choose a unit that matches your pound's total gallons, and wait and see if it is enough. When the fish outgrow the bio-filtration, then you can keep what ya have and connect another bio-unit.
Heh, sorry. I don't know of any better way of pin pointing it. If I were you, then I would choose the system model that properly matches your potential, after a few years, total of 139 pounds of fish.
Good luck! :goldfish:
((side note #1: bead bio-filtration units work much better if you have a mechanical filter unit cleaning the water of debris before the pond water goes into the bead filter))
((side note #2: supposedly the bacteria in the bead filters work better when the KH is at 200 or higher due to the high volume of nitric acid produced inside the unit ... i'm not entirely convinced on this though))
((side note #3: all these bacteria actually do occur naturally ... do not need to add any specialized bacteria products unless you feel otherwise))
