Moving bed fitlers are a popular option in filter system designs. As a result, many ask how much bio media or K1 specifically do I need. In many cases the ponder already has a tank and want’s to know how much media is needed to fill the tank. Generally the response back is “you can never have enough” or fill a MB tank in the 50 to 60 percent range with media. Unfortunely, this is working at the answer from the wrong side. It doesn matter what size tank you have on hand, how big your pond is or the size of your other filter components. Just because you have a big SC, doesn’t mean you need a big MB.
A more logically approach in designing bio needs is to look at the amount of fish food that needs to be processed base on the number and size of the koi in your herd and how heavy you will be feeding them. Unfortunely there’s limited documentiou out there on how to go about this. EA, the distributor of K1, has provided online, some broad guidance on how much K1 is needed, based on their Nexus filters.
The data is in metric and converting it to U.S. standards scares many of us…it’s math. So here’s EA’s quidelines, converted.
So now a lesson in what you are seeing. You have 14 koi that are 24” in length. There are a number of sites that contain koi length/weight charts and I found that 6lbs is average for a 24” koi or a total 84lbs of koi in the pond currently. You’re providing a moderate level of feeding…1.5 percent of the total koi weight. You find the 83lbs in the 1.5% body weight column and follow the row to the left to see that this would be almost 18 oz of feed per day. So the suggested amount of K1 would be 2.4ft2. While this is just a ball park figure, it’s better than a flat out guess. Next question is going to be, how big a tank do I need. Rounding the K1 to 3ft2, it would take up about 22g in a tank (7.5g per ft2 of K1). With a 55g barrel, this would be less than a 50% media fill rate but would give you room to add another cubic foot of K1 later to get to a 60% fill ratio. In sizding bio needs, you really need to look at your herd now and in the future. Is the herd stable in numbers and size or will it be a growing herd that will require additional bio capabilites. That brings in the ideal of sizing a tank for later use but filling with the amount of K1 for today’s situation and adding more K1 later. I feel that these quidelines would also work for Bioflow9 which is similar to K1 in size, shape and the amount of surface area it provides.
Edit: Koiphen member shortypen has some bio filtration design concepts on his website. It includes a section on calculating K1 amount. It's a very streamlined calculation process based on fish load and feed.
His K1 calculation is in the sub-section "Designing Koi Pond Bio Filter"