Art by Alexander Vasiljev, Copyright © 2017


Wednesday, August 13, 2014


Having started with a DIY bio filter located in the separate tank (see "Before The Fish") and understanding more on how it works, I later added a UV sterilizer and a fine filter bag to further improve the quality of my water (see "Filter Box Additions And Improvements").

Although, the filtering system have been working perfectly, apart from an accident caused by not cleaning it often enough (see "Distracted, You Must Not Be"), I have been thinking about simplifying my filtration process. I was also looking to reduce additional maintenance apart from 100% water changes. So, I came up with a different design. The new filter design ended up to be a combination of submerged "canister filter" and bakki shower, used in koi ponds.

I started up with making an acrylic box to fit the pond's width. The box is only 3.5 in (9 cm) wide measured inside and 11 in (28 cm) high to fit in 12 in (30.5 cm) high pond. The front and back walls of the box were not joint with the bottom, leaving spaces for the water to escape.

I filled the box with layers of media - Eheim Substrate Pro in the bag on the bottom, followed by Matala black matt, followed by Bio House Cylinders covered with another layer of Matala black matt. All media has a tremendous surface area for beneficial bacteria to grow.

Front side view

Bio House filter media cylinders are made from mineral stones and silica

I placed my new bio filter in the pond and left the to "seed" with beneficial bacteria for three weeks, after that, I could safely replaced my old filtering system with the new one. So, how it works?

On one side of the pond, I placed submergible pump with pre-filter sponge intake to move water through the UV sterilizer to my submerged bio filter box.  

Set up top view

Water than is sprayed on top of the filter, floats down and exits at the bottom of the filter box. Simple.

Here are the benefits I find so far. Due to the wide opening on the bottom of the filter box, where the water escapes, the flow is very gentle and the water is almost still, although it is pumped at 600-700 gph (2500-2650 lph). A big improvement from my previous design. Next, the cleaning has become much more simple. The filter box is accessible from above and the media can be pulled out easily and rinsed in the same pond water before 100% water change, making it a breeze. Having major parts of the filtering system inside the pond have minimized the danger of water leak. I also see a huge esthetic benefit. Freeing the space from 30 x 12.5 x 24 in (76 x 32 x 61 cm) box on the side of my pond in my small apartment is a big deal.

Subsequently, with this change, I lost an extra 30 gal (113 L) of water and 4 in (10 cm) of pond's length. Though, the loss in length is not that important, considering 8 ft (2.4 m) long pond.

After placing the filter box inside the pond, I found gaps on three sides of the filter box due to pond's curved angles. Knowing that my ranchu will venture into these narrow spaces, I filled them with Matala mats, adding more bacteria friendly surface. To avoid stale water between the back wall of the filter box and the wall of the pond, I installed four air stones for circulation. Also, the gap is large enough to place an extra bag with bio media, as seen in the image below. In which case, the water is moved through the media by air bubbles.

All it left, was a cover to make, concealing the filter and voila!