pond filtration

Likely the most discussed aspect of the hobby, a filter is essential for 2 reasons. One is to keep the water visually clear so you can enjoy your fish. But more importantly, filters keep the water chemically clean. Fish release toxic ammonia and that needs to be quickly converted to far less toxic nitrate [plant food] before it builds up to troublesome levels

Remember, clear water can be toxic to the fish while dirty water may be chemically perfect for them. Ask anyone with a successful pond and they will tell you, a properly functioning filter is pivotal

The challenge is making the right choices because there is so much conflicting information, particularly on the web. The bottom line is, all filters have their strengths and weaknesses and there is no panacea despite what some will claim

bakki shower

Bakki Shower

on one of our tanks

What Does a Filter Do ?

Filters mechanically clean the water by removing particulate with various foam materials, beads etc. Filters are also homes for nitrifying bacteria Nitrosomonas,Nitrobacter and Nitrospira are chemolithotrophic bacteria that oxidize Ammonia and Nitrite for energy and fix CO2 for their carbon source. These sessile bacteria require surface area - so medias that offer more area in theory will house more bacteria. These bacteria are essential to a healthy pond and do occur naturally. The problem is, our "fish ponds" produce too much ammonia and therefore require extensive seeded filter beds in order to process it all - or risk hurting the fish. The biggest mistake I see is people cleaning their filters with a hose. This cold, chlorinated water is designed to kill bacteria in drinking water and therefore, it damages beneficial microbes even thought the bio film is pretty tough
kaldnes media comparison of new and fully seeded K1

The water flowing through the filter brings oxygen and food [nitrogen] to these bacteria. This aerobic bacteria require large amounts of oxygen so aerating the pond and filter is a highly recommended. Surface area, nitrogen load, phosphorus, temperature and water chemistry will ultimately control bacterial population levels. If given their druthers, bacteria we want to cultivate like a higher pH, decent KH level for buffering and warm water over 20 celsius

  • Sponge filters are great for biological and mechanical filtration - safe for fry
  • Crud builds up surprisingly fast - bottom "filter rocks" just make it harder to clean
  • This is an overflow type filter that has to be positioned above the return
  • Vortex tanks settle out large debris before it gets to the polishing tank


Kaldnes Filter

Design Concepts

A good basic filter design will incorporate at least 3 chambers - settlement, polishing and biological. Probably the most important feature of a good filter is the settlement chamber. When I started in the hobby I thought a large chamber with nothing in it would be useless. However, a vortex chamber is pivotal and to work effectively should allow sufficient dwell /residence / retention time for debris to sink to the bottom

Dwell time is the length of time water will remain in the drum. If the dwell or retention time is too short, debris will just continue onto the next chamber. It is therefore imperative to realize that a faster flow rate is not always better. A 3 minute dwell time would be a bare minimum, giving the debris at a chance to sink. When you do the math you can quickly see how big these chambers have to be. A 3000 gallon pond with a 2000 gallon flow rate filter system would require a chamber at least 100 gallons. The math is as follows - 2000 gph divided by 100 = 20. 20 turnovers divided by 60 minutes = 3 minutes/turnover. Another guideline is to look at the volume of the vortex. If you divide that by 4, you will get a gpm flow rate. So a 200 gallon vortex / 4 = 50 gpm - 3,000 gallons per hour

Sieves are another viable first chamber option to remove solids from the pond. Remember however, particulate can settle down to about 100 microns in size. Your sieve screen may only trap particulate down to 300 microns. So with the right flow rate, the potential for the vortex to remove smaller particulate is an advantage over a sieve

Properly manufactured vortex tanks allow for smaller chambers to be utilized because their design is tuned for settling particulate. All filters should have a gate valve installed which allow the isolation of the filter from the pond. This is necessary for effective cleaning and medicating
Crud builds up surprisingly quickly in a properly sized vortex

Poorly constructed filters use foam as the initial filter media. Unfortunately the foam is quickly saturated by debris. This means the flow rate [return to your waterfall] slows down and you will need to clean the filter very frequently. In a properly designed 3 chamber filter, the foam goes in the last chamber so that it only has to trap small debris - larger particulate has already been settled out. Therefore much less frequent cleaning is required and water re circulation remains at peak rates

Some companies claim that natural filtration with rocks on the bottom of the pond and waterplants are all your fish will require for a healthy balanced eco system. The truth is however, you can't rely on a natural process in a unnatural setting. A backyard pond is not a natural thing. No one I know is willing to keep 1 fish per 10,000 gallons+ so natural approaches will fall short. Sure a food web [albeit truncated] will develop in any pond but it is not extensive enough and in balance to cope with the abnormally high fish load. The higher one goes in the food chain in nature, the lower the population of the apex predators. Not the case in the backyard pond

As an example, zooplankton are essentially going to be wiped out due to over predation by the fish. They will survive in greater numbers when plant material is available. But koi do eat a lot of plants too and typically our ponds are not planted heavily. So, instead of having a a foundation web of plants and zooplankton, the environment will not support it. This is why so many UV's are sold [zooplankton eat green water algae aka phytoplankton and will do better with less predation and macrophyte cover]. Marketing hype tries to tie nature up in a pretty bow - it just doesn't work like that. more information is available here

Flushing a 4 foot Vortex

See more of Tony's pond on our videos page - that pond show