Likely the most discussed subject in the hobby is filtration and for good reason. Although opinions vary as to what works best, all can agree that some sort of filter needs to be installed in every pond for long term success
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
Most of the focus in the hobby seems to be on bio-media performance. Perhaps more attention should be paid to effective solids removal and a simplified maintenance regime
Do I Need a Filter ? In one word, YES. A good filter is an essential piece of equipment for your pond. Filters perform 2 main functions. One is to keep the water visually clear so you can see your fish. But more importantly, filters keep the water chemically clean. Fish release toxic ammonia and that needs to be converted to non toxic plant food.
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. Filters should be easy to maintain and by design, never clog (which slows down the flow rate)
What Does a Filter Do ?
Filters are for the most part, homes for nitrifying bacteria. But other types of bacteria will propagate the filter and benefit the pond as well. Filters in essence chemically and visually keep the pond water
clean
The bio-media within the filter provides surface area for sessile bacteria to adhere to. The more surface area, the greater the number of "potential" bacteria. The water flowing through the filter brings oxygen and food [nitrogen] to these bacteria. Surface area, nitrogen load, temperature and water chemistry will ultimately control bacteria population levels
Simply put, the bacteria convert the toxins released by the fish into far less toxic plant foods. Your filter should also be effective in removing particulate from the water. This is achieved by allowing heavy detritus to settle in the first chamber. A vortex is utilized here to help facilitate the sinking of solids to the bottom of the tank for easy flushing
Read more about this in Design Concepts below
Do It Yourself or Store Bought ? Home built
As with all choices in life there are always pros and cons. In general, making your own filter is a good option if you are handy and do your research. They also afford a level of customizability that a store filter can't match - you can build for the exact specifics of your site. Home built filters are usually less expensive and if constructed properly, provide equitable results when compared to the pricier store bought units
Store bought filters
These
do offer some advantages. They have manufacturer support, usually a better finished look and are easier to setup. But consider proven full size units only. The less expensive store bought filters ie. in pond box and small pressure filters - are excessively overpriced, fundamentally flawed and maintenance nightmares. Value is what you are after
Settlement Tank Home Built
Typical external store bought overflow filter
nitritech tritech 5000. Nitritech is now out of business but sold their molds to a company in the US
Design Concepts
A good basic filter design will incorporate at least 3 chambers - settlement, biological and polishing. 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. 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 proper cleaning, medicating and Winter shut down
Poorly constructed filters use foam as the initial filter media. Unfortunately the foam is quickly saturated by debris. This means the flow rate (ie 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 recirculation 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. It's a small closed system with an extremely high bio load and our goal is that everything survives which of course goes against the laws of nature. No one I know is willing to keep 1 fish per 10,000 gallons+ so natural approaches will fall short. Sure a microbial web will develop in any pond but it is not extensive enough to cope with the abnormally high fish load. Rudimentary science debunks this marketing myth espoused by companies who just want to sell you and make it sound so easy. As with keeping all animals, hygiene is important. If you keep a rabbit, budgie or guinea pig you have clean the cage. Assuming the natural breakdown of the high excrement load will occur in a fish pond is a mistake.
A quick tip: if you are purchasing a filter and it readily fits in the backseat of your car, it's likely not well designed to filter your pond
1
vortex tank
A bottom drain and vortex are the key elements required in an effective filter system. The bottom drain is really a misnomer as it is essentially a 24/7 vaccuum, constantly removing settled debris into a vortex for easy flushing
If you are pumping the water to your filter from the pond you will not be able to remove this larger settled debris
Additionally, a pump in the pond will get clogged over time decreasing the turn over rate. Debris that manages to go through the pump will be broken down into smaller particulate making it harder to settle
Bottom drains are the best way to keep the bottom of the pond clean and help maximize water movement throughout the entire pond - but they need to supply a vortex tank in order to get the real benefit
The amount of debris that settles is amazing
Pictured
left is a 300 gallon vortex. It has a conical shaped bottom to allow proper flushing of accumulated debris. Although initially expensive, it is a lifetime purchase that does not require maintenance and doesn't break down - well worth the investment
Video on a Filter Utilizing Kaldnes
The internals of a standard
pressure filter showing the reticulated [open cell] foam
and bio balls
This filter system is more
ambitious with a couple of pumps, UV, valved jet return and a 3 chamber vortex system
Gravity Fed Filter Systems
I consider gravity fed filter systems to be fundamentally sound and proven. Every pond should have a gravity fed system in place and the addition of other complimentary filter types should be strongly considered. Other systems can work but as a general rule, require more maintenance to acheive an inferior result
Recommend Filter Types Bead filters have there merit but there are caveats. They still require extensive settling and pre-filtering before water is pumped through them - clogged pumps and extra maintenance will occur if they are not setup properly. BF's are excellent for small particulate removal and biofiltration - a nice complement to a gravity system. As they clog the flow rate is reduced therefore Bead Filters need to be monitored
and cleaned regularly
Trickle towers, used previously for marine tanks more than ponds, towers are in vogue now and do provide a super saturated biobed with a small footprint. They are great at removing nitrites. Because the media is not submersed, the bacteria will not survive long if the water stops flowing through the tower - something to watch out for
Rotating media filters offer very good nitrogen conversion and are inexpensive and easy to build. We install these on many of the higher end ponds we construct. Its hard to find a negative with these types of filters
Chart of Common Methods of Filtration and their Advantages & Disadvantages
A Sump Pump in the Pond Recirculating the Water
initially inexpensive [although running costs are high]
easy to install
no real filtering - the biggest disadvantage of all
aesthetics [pump, cord & tubing is visible]
pump clogs with debris and flow is reduced
difficult to clean
danger of sucking in fish
danger of electric shock to fish
short life of motor [not designed for continuous use]
Pond Pump in the pond with Sponge Prefilter, Foam on a Pipe or Internal Box Filter
inexpensive [but overpriced for what it is]
easy to install
some filtering ability
okay performance for small ponds
danger of sucking in fish reduced
very high maintenance if filtering [filter clogs easily]
some foams do not filter particulate (therefore do not clog)
have to be removed from pond to clean
units overpriced for what you are getting
minimal filtering ability
when filter dirties the flow slows down
aesthetics [pump, cord & tubing is visible]
pump eventually clogs with debris
difficult to clean
danger of electric shock to fish
Pond Pump in Pond with External Pressure Filter (ie. Laguna, Cyprio etc.)
decent bio filtering
small solids removal
capable of filtering small ponds only (<1,000 gal.)
install is easy
small footprint [easy to hide]
very high maintenance due to filter / pond size ratio
units overpriced for what you are getting
proprietary parts are expensive if broken
when filter dirties the flow slows down
aesthetics [pump, cord & tubing is visible]
pump clogs with debris
difficult / time consuming to clean
danger of electric shock to fish
danger of sucking in fish
Pump in the pond with Overflow External Filter
good filtering
easy to clean
bypass keeps water flowing at full capacity
small footprint
aesthetics [pump, cord & tubing is visible]
pump can clog with debris
danger of electric shock to fish
danger of sucking in fish [unless prefiltered]
External Retrofit gravity Fed filter system with Mid Water Feed
excellent filtering
easy to clean
good choice for retrofitting existing ponds
no equipment visible in the pond
can use energy efficient external pumps - no pump clogging issues
less frequent maintenance
larger footprint can be harder to hide
more expensive [but better value]
does not remove all debris like a bottom drain
usually requires professional help to install
External Gravity Fed filter system with proper 4" Bottom Drain
excellent filtering ability
good water clarity
good water quality
can use energy efficient external pumps
easy to clean
no equipment visible in the pond
rare pump clogging issues
less frequent maintenance
larger footprint can be harder to hide
more expensive but better value for the dollar
usually requires professional help to install
One can see the trend of Advantages increasing and Disadvantages decreasing as we move down the above chart. Additionally, moving down the chart means increased costs, time and space are required. The key however, is the value for the effort is much greater. Water quality and clarity are much improved, maintenance is dramatically reduced and the fish will be healthier and grow faster when you invest in the proper system
