What Can You Use for Pond Filter Media, and How to Layer the Media?

The range of materials available for use as pond filter media is pretty large, and it keeps getting larger every year. This article will review some of the more common choices that you have, with an emphasis on their use for pond filter applications.

There are several factors to consider when choosing filter media for your pond, including but not limited to:

Physical properties (size, weight, etc.) – Materials that are too small or too light may be easily displaced by the water currents in your pond. Of course, if they’re too large or heavy they won’t settle and provide proper filtration.

Accumulation of solids – If the material absorbs a lot of debris, it may need to be cleaned regularly to maintain an efficient pond filter.

Physical structure – Make sure the materials you choose aren’t going to get clogged or jammed by larger debris, and they’re not so large that their physical structure interferes with the filtration process.

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Performance – The material must be able to handle the number of solids being produced by your pond, and you should consider any risks posed by the type of material.

What can I use for pond filter media?

Here are some of the more popular options for pond filter media:

Carbon

This is one of the most common materials on earth, and it’s used in everything from toothpaste to fuel cells. It’s a good medium for ponds because it’s very fine, lightweight, highly porous, and inexpensive. The primary downside is that carbon does not accumulate solids, so it needs to be cleaned regularly to maintain performance.

Coconut Fleece

Coconut fibers are a great option for pond filter media. They’re very lightweight and absorbent, and fairly inexpensive. The downside? They’re not normally available in local brick-and-mortar stores, but there are several online sources.

Coconut fibers are also used for water filtration in third-world countries, where they’re often dried and burned as an inexpensive fuel source.

Pine Bark Nuggets

Pine bark nuggets are a popular choice because they’re easy to find locally (ask at your local garden center), reasonably lightweight, moderately absorbent, and will not normally accumulate solids. It’s important that you make sure the pine bark is kiln-dried, which will eliminate the risk of fungus or other contaminants developing in your pond if otherwise allowed to remain damp.

Diatomaceous Earth (DE)

This substance is mostly composed of fossilized diatoms. It’s very fine and highly porous, making it an excellent filter media. It’s also inexpensive, has a low weight density, and won’t normally accumulate solids. However DE is very light (which can be both good or bad), and it may not settle as readily as you’d like into a pond.

Cotton Batting

Cotton batting is another fiber option, but in this case, the fibers are attached to a cotton backing that helps them remain intact during use. The batting can become quite heavy when wet, so you’ll want to keep that in mind if your pond isn’t equipped with an overflow system. Cotton is gentle on gills and will absorb a lot of debris without overloading the physical structure of your pond filter.

Glass Beads

This is actually a misnomer, as glass beads are not naturally round – they’re manufactured in cylinders and then ground down into whatever shape you’d like. Glass beads have many of the same properties as diatomaceous earth (DE), including moderate weight density, high porosity, and low accumulation of debris.

The glass must be chemically inert to avoid leaching chemicals or other harmful materials into your pond water. There are several different sizes available depending on your specific needs, and occasionally it’s possible to find them locally for use in fish tanks if those are local businesses rather than online-only shops.

Like DE, these beads tend to be very light compared to other filter media options.

Crushed Oyster Shells

Crushed oyster shells are a great choice for larger ponds because they’re inexpensive, easily obtainable locally (ask at your local fish store), and won’t normally overload the filtration system.

Oyster shells are very lightweight, have moderate porosity, and won’t accumulate detritus on their own. The only setback is that you may need to replace them more frequently than other options depending on your number of aquatic inhabitants.

Aquarium Gravel

There’s a reason aquarium and pond companies sell gravel – it works! The big advantage of gravel over other pond filter media is that it stays put rather than accumulating in one spot or another within the filter system.

That means you’ll not only see an improvement in water clarity from the extra surface area, you’ll also see an improvement in your filtration efficiency as the gravel works to catch debris.

However, it’s important to choose gravel that has been specifically designed for aquariums, there are several options out there that have UV-inhibitors added which may be harmful to aquatic life.

Peat Moss

This is another soil additive that can work well as filter media in certain circumstances. Peat moss is very absorbent and will not normally accumulate detritus on its own (although it still needs regular cleaning).

It’s lightweight and easy to work with, making it a good solution for smaller ponds or those without room for larger sizes of media. The biggest drawback? Peat tends to float when wet, so if you have a moving water feature you may experience reduced levels of filtration efficiency.

Crushed Limestone or Dolomite Lime

Crushed Limestone or Dolomite Lime is more commonly used in larger ponds with very high fish counts, as it provides a solid mass that will not accumulate detritus on its own and can be rinsed out regularly without overloading the system.

However, if your pond has just been established or has very low numbers of fish the limestone might simply stay below the surface where it won’t do much good for your system. There are other dissolved minerals in limestone which may leach into the water, so be sure to research this option thoroughly beforehand.

Rocks with Abrasive Edges (Marbles, Slate)

The best way to cover the surface area of your pond filter media is with round material, which will catch debris and hold onto it until you remove it for cleaning. However, if you have a smaller pond where space is an issue or larger rocks are too heavy, then marbles or slate can be an excellent alternative.

The advantage here is that these materials are already fairly inexpensive and usually locally available for use in fish tanks or water features as decoration.

Low-density Polyethylene (LDPE)

Made from recycled plastic bottles, LDPE has moderate density and moderate porosity levels. This is often used as another decorative option due to its unique ability to reflect light into the pond while still being safe for aquatic life – there’s even some evidence that this material can help to reduce algae growth.

Prepared filter media

Commercially prepared filter media that has been designed specifically for use in pond filtration systems is often your best bet, however, there are several DIY options available if you prefer to avoid buying new materials every time you clean out your filter system.  As I’ve seen above they don’t all have the same advantages, so choose carefully before deciding on what’s best for you.  

How to layer pond filter media?

The most important thing to remember is that your filter media needs a place for detritus and debris to settle on – if it can’t settle, it will be released back into the water and continue its journey through the pond until it can.

As always, there’s no one-size-fits-all solution to this issue. Here are a few suggestions to get you started on the right track:

  1. Polystyrene balls – These are often used in Koi ponds as decorative options that will collect debris when rinsed out regularly. Use one layer about two or three inches thick.
  2. Granular Activated Carbon (GAC) – This is perhaps the most common filter media option for larger ponds. It’s important to note that you shouldn’t use your GAC filter as a house for fish, and leave a few inches between it and the surface of your water. Use two or three layers about an inch thick.
  3. Poly fiber filter pads – These can be placed directly onto the bottom of your pond, or underneath GAC media. You can leave them there permanently as they do not absorb detritus and will catch larger objects before they settle on top of your other filter system components.
  4. High-density Polyethylene (HDPE) – Very similar to LDPE filter material, it has one important difference: HDPE floats in water! Be careful when placing this beneath a waterfall so that smaller pieces don’t get washed away. Place two or three layers about an inch thick.
  5. Sand – Sand is most commonly used for catching detritus before it sinks down and settles into larger systems. You’ll obviously need a place for it to go so make sure you have your pond design taken care of before you purchase sand.
  6. Living plants – The best option for a natural, “self-cleaning” filter, but be sure to choose species that are suitable for your water temperature and pH level.

The list goes on and is entirely up to you how many layers and which materials you use in the system. If in doubt start with two or three levels of increasingly dense filter media and figure out what works best for your individual needs later on in the game.

You can always adjust from there depending on how often (or infrequently) you clean everything out. Once again though – don’t over-complicate things with unnecessary layers, these are just a few popular options to consider.

Remember – fish can’t live in water that isn’t suitable for their habitat. Creating a natural ecosystem within your pond ecosystem will ensure that they have the best possible quality of life and you’ll be enjoying them for years to come.

Summary

Ponds have a lot of benefits to offer, but they can also be expensive to maintain. As you may already know, the average pond filter system can cost anywhere from $500 – $4,500.

That’s why it’s important that you take your time when searching for one and consider all the options available before making any decisions. It doesn’t matter if you’re looking into DIY or purchasing new materials every few months – there are many different types of filters out there with varying levels of efficiency at capturing debris.

The most important thing is remembering to place them somewhere where detritus and other pieces will settle so as not to cause problems in your water quality later on down the line.  This should help guide you while shopping and give you an idea of what to expect.

From here you should be able to make an informed decision about which type of filter system will work best for your pond.  Remember, this is a huge investment that won’t require maintenance for decades if maintained properly so take the time to find one that fits with your needs and offers years of enjoyment.