Pond Filters Explained

A pond filter is one of the most important parts in a good backyard pond design. If you have fish, regardless of whether they’re koi, goldfish, or anything else, a good filtration system is critical.

Mother nature uses plants and other natural elements to filter water, and for any small ponds, aquatic plants can certainly be helpful in acting as filters. One might say they were the first really good pond filtration system! It’s suggested by many experts that you’ll want to add around 70% coverage of plants for them to adequately filter a fish pond on their own.

Many modern day pond owners may like plants, but they often prefer to not use quite so many, and in that case some type of physical filter will be necessary. There are two very common designs that you’ll find not he market place as well as a number of home made DIY pond filters that you might want to make yourself.

All of these pond filters are based on some fundamental processes that help clear the water of substances varying from debris, such as leaves, grass clippings, and any number of solid things that might fall into the pond. Another problematic thing that some filters help with are the unseen substances in the water such as ammonia and nitrites. These can build up as fish waste, among other things, are broken down via the nitrogen cycle.

Pond Tip: If your pond get’s a lot of debris in it, such as leaves, consider installing a pond skimmer which can capture a lot of this stuff before it get’s to the filter.

The Mechanical Pond Filter

pond filterThe most common and simple pond filter design is the pure mechanical filter. These are most often used in very small ponds and those that do not contain fish. As the name implies, a mechanical pond filter has various filtering pads and substances in it that will strain anything large enough to get caught, out of the water. You’ll find filter and pump combos which can be placed at the bottom of a shallow pond. Water is drawn in by the pump, passed through the filter pads, then either sent back out into the pond or sent up a small fountain.

Mechanical filters will inevitably need to be cleaned out routinely and the variable of how often is usually determined by either the amount of debris one get’s in a pond or the amount of algae growth that a pond may experience. All of these can be captured by the filter if they’re big enough.

Mechanical pond filters should be looked apron as a good tool for removal of solids, however they do have their limits. They will do nothing for the reduction of things like ammonia, which is why we always suggest the use of a biological filter (or numerous pond plants) if you have fish.

The Biological Pond Filter

biological pond filterA biological pond filter is a more advanced filtration system than any other filter. There is a mechanical component in many of them but in addition to that, there is also a biological part that does some very important work. By the term “biological” what we mean is that beneficial bacteria (a natural occurring critter) is provided a home in the filter and these good micro bugs help clean up any organic things in the water which includes both the solid material, and the unseen substances as well.

In their work, bio filters create a much cleaner pond in terms of a physical appearance but they also create cleaner, healthier, and more balanced water. This helps create a safer environment for fish and can even help limited unwanted plant growth such as algae.

In the world of biological filters you’ll find a wide range of designs. Some of these can be very expensive such as the pressurized bead filters which are much like a pool filter. They are self contained, never need cleaning, and use a backwash feature to clean out debris.

On the other end of the spectrum is the home made pond filter, made out of a plastic tub or barrel. These have all the components needed to filter the water and they contain a bio-chamber that houses filter media, which is nothing more that some type of material (scratch pads, plastic coil, bio-balls, etc) that provide a home to the beneficial pond bacteria.

Several key points about using a biological filter include making sure you know the gallon capacity and total fish loading in your pond. A filter must match or exceed that capacity in order to work well. Manufacturers can help in estimating this need, and with a little research you can be assured of a good fit with your pond.

UV Pond Filters

uv pond filterUltraviolet pond filters are not a filter in the truest sense of the word like our first two examples. They don’t really filter anything out of the water however they can be useful for some pond owners.

Green water algae is a problem in many fish ponds and uv light is one of the best ways to deal with the problem. This type of pond algae is actually very small, single cell algae, that are free-floating in the water. In very small numbers you wouldn’t even see them, however as they build up, they begin to tint the water, sometimes dramatically.

Many of these algae are so small that they may pass through a normal filter system. If that’s the case you may not see much of a change at all. However uv light is designed to damage algae, and in a sense sterilize things that pass in front of it. This will either kill or damage the algae cells which makes them clump together in bigger groups. This process will then allow a decent filter system to pull them out of the water, and if it’s a biological filter, the good bacteria will help break down the dead algae and get rid of it.

Ultraviolet light is also good at killing some pathogens and viruses that might be found in fish ponds and many koi pond owners use them for that purpose. Key points about the uv pond filter include getting a unit that’s well matched to your pond size, as well as making sure that the bulb or lights are changed as suggested by the manufacturer, and that the flow rate through the device is frequent enough to all the gallon volume of the pond to pass through the filter numerous times through the day.

You may find some pond filter models that include a uv light along with a biological filter system. Or, you can add these components together separately as you need them. Certainly not every pond will need uv but should you run into consistent green water issues, it might be worth a try.

In the end, if you find yourself struggling with maintaining good water quality in a pond, have fish health issues, or algae control problems, the pond filter would be one of the first places to look to improve many of these things.

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