I love having a pond. There is nothing better than sitting and watching your fish swim about.
To get to this point took me a lot of research, some fairly bad DIY projects, and plenty of sweat and hard work.
Is it worth it – it sure is.
Today I want to show you how to make a small pond filter that takes care of both mechanical and biological filtration. There is not a whole lot to the filter itself but it does wonders for your pond health and clarity.
Here is a quick video showing it in action before I added the filter media.
Now don’t get me wrong here – this is for a small pond or water garden that you can customize to suit your needs.
If you have a large volume of water in your pond then check out my homemade pond barrel filter.
I have a large filter system on my Koi pond already so am going to use this after the skimmer and UV clarifier to filter out some of the finer particles in the pond.
You could however load it up with filter pads, lava rock, bio balls, or any other type of filter media with a good surface area for beneficial bacteria to grow. The options are endless really and all you really need after that is a submersible pump and a length of flexible pond pipe.
Ok, so let’s get started on this small pond filter.
Easy to make pond filters
First up you are going to need a plastic tote for the box filter. I picked this up in the local hardware for a few dollars but you can get them almost anywhere – just go for a heavy-duty one because you don’t want it to crack when full of water.
This box filter holds about 16 gallons of water so would make the perfect filter for a small pond or water garden.
The first thing to do is measure do 1 and 1/2 inches from the top center of the filter box and use a hole saw to cut out a 25mm hole.
Make sure to remove any rough edges from the new hole and prepare your tank connector. I am using a 1-inch white waste pipe for this filter but you can experiment and come up with your own design here.
When installing the tank connector make sure you have the rubber gasket already in place before you push it through the hole. The plastic nut goes on the outside of the filter box.
The reason I use these is that they have pressure fit connectors and makes it easy to dry-fit everything before final assembly.
Next up you are going to need 2 90 degree bends, a T-piece, and 3 x 2inch long pieces of pipe. This will form the first part of the inside of the pond filter spray bar.
When assembling this section of the filter first insert the two pieces of pipe into either end of the T-piece and take note of the measurement.
Go ahead and dry fit the rest of the parts together and push the small piece of pipe coming out of the middle of the T piece into the tank connector. This should hold everything in place for now.
Next up you are going to need 2 longer pieces of pipe for the spray bars. Cut these about 20 inches in length and set them to one side.
Using the measurement you took a min ago cut a small length of the 1-inch pipe. and add a 90-degree bend to each end. This will form the other end of the spray bar and help keep the pond water in the system and saves you from cutting any additional holes in the filter for support.
Next, you need a length of 1 1/4 inch pipe to act as a support for the other end of your spray bars and to drain the water back to your pond.
Measure down 2 inches from the end of the pipe and use a 1-inch hole saw and cut all the way through the pipe. Slot your smaller pipe through this and add a 90-degree bend to each end.
The last thing you need for this part of the pond filter is a 1 1/4 inch t-piece for the other end of the pipe.
Dry fit everything together now and make the required adjustments to the long 1 inch pipes are level and the end of the t-piece is about an inch off the bottom of the filter base.
Make a mark on the sidewall of the filter box around the end of the tee. measure down 3/4 of an inch from this mark and this will be the center hole for your next job.
Take a larger hole saw and cut through the side of the plastic tub. You are going to need a uniseal for this next bit.
Insert the uniseal from the outside of the box and make sure it sits flush. Push a spare bit of 1 1/4 inch pipe through the uniseal and into the tee.
This will now hold everything firmly in place with the bottom of the tee about an inch off the base of the filter. This is important because that’s how the water gets out and back into your pond. The mechanical and biological filtration happens above.
Once you have everything looking good it’s time to take it apart again. We need to make a way for the water to get into the filter from your pond pump.
For this take the two longer lengths of 1-inch pipe and draw a line with a pencil the length of each pipe. Draw a series of marks along this line – every inch or so from one end to the other.
Take a small 3/16 drill bit and drill holes on each of the marks on both pipes. Now draw another set of lines on each pipe about 1/2 inch away from the first one. come in 1/2 inch from the end and make a mark. now add marks every inch along the pipe.
You should end up with marks that alternate with the set of holes you drilled a few mins ago. Drill along the pipe again on these marks – both pipes – and then get some sandpaper and clean up all the rough edges.
Dry fit everything back together again and your pond filter should look something like this.
Setting up your pond filter
Every filtration system is different and every pond and water garden has different filtration needs. The first thing to do is work out how many gallons of water are in your pond and design your filtration around that number. When starting our pond filters are a must-have to help balance out your pond water.
You can choose from submersible filters that sit at the bottom of your pond. Some even have a built-in pump but you then have to deal with a power cord coming out over the side of your pond. While these are easy to install, submersible filters have to be removed from the pond to clean them.
You should always base the size of your filter on your pond size. Are you looking to power a pump and fountain or perhaps an all in one pump filter combo? Whatever you decide on a good bio filter is the difference between a healthy pond and a deadly pond.
Mechanical and Biological filtration
The whole purpose of your filtration is to clean your pond water. Some of the best pond filters on the market can do a great job but also cost you a small fortune, plus there are so many options out there that your head would melt trying to figure out the best filter for your pond.
The mechanical filtration removes the solids from your water. The quicker you can remove these from your ponds the less chance they have to break down and cause issues with your water quality.
The biological filtration in your pond filter converts these nasties into harmless nitrates as part of the nitrification cycle that happens in a healthy pond. Beneficial bacteria colonize on your filter media and the walls of your pond – well, pretty much everywhere in your pond and slowly break down the waste.
Water flow rate is very important for your filtration system. You need a pond pump that can cycle your water every hour or so. You also need pond filters that can cope with the waste load in your pond.
One issue we see all the time is the pump is either too weak for the filter system and too small for your ponds or it’s too powerful and moves the water too quickly before the filters can do their work.
Adding a diverter valve or a ball valve to the pipework allows you to easily control the flow rate of your water in and out of the filters. There is heaps of content online about this topic so do your research.
Adding a UV clarifier to your filtration does nothing to clean the waste out of your water but it does help combat green water. Green water is caused by a build-up of green algae in the water. Whilst it does no harm to your fish – they actually like it – it does ruin the view. A uv light is a quick way to clear up a green pond, but the ultraviolet light also helps remove some of the nasty bugs from the water as well. Read more about green pond water.
One of the brands we like is Oase. They produce awesome UV light options for ponds of all sizes.
The whole idea of a pond filter is to provide mechanical and biological filtration and to clean your pond water. There is an endless list of filter media like bio balls, K1, etc, to choose from but here is a breakdown of a few of our favorites.
Bio Balls are a great option because they provide a huge amount of surface area for beneficial bacteria to colonize. This bacteria is what removes the nitrates from your pond water – deadly to fish if left unchecked.
Filter pads are readily available in all shapes and sizes. I like to buy mine in larger rolls and cut them to size. I’m using fine filter media for this filter box because I want to try and remove the finer floating debris from my water. You can get different grades of filter media from very coarse to fine. These are often layered on top of bio media in a pressure bio filter or a submersible flat box filter setup.
The coarse filter pads make a great home for beneficial bacteria and provide plenty of surface area for these to grow on. Often called Jap Mat you can pick it up in any decent pond supply shop or here on Amazon. You often see the filter kit packs with three different color pads. They are very easy to install and work wonders to clean your pond water.
What is the best small pond filter?
This really depends. For a small pond, you want something that is easy to clean out and compact enough that it does not take over in your landscape.
Most of the time you are going to be stuck for space. The key things with any pond filter are biological filtration and the ability to mechanically remove fish waste from the water.
Does a small pond need a filter?
When a pond is new it is advisable to install some sort of pond filter. Over time your pond will balance out and the plants when they mature will start to remove the waste from your water. You often see ponds with bog filters installed. These are just an area of the pond that pumps through the root base of plants to remove waste.
What is the best pond filter system?
This really depends on your pond and your fish stock. Pond filters, especially ones you buy are all rated based on the size of your pond. For example. You could have a pond of about 500 gallons and when you go online you will find a pond pump and filter combo with a built-in uv clarifier that is rated for ponds up to 500 gallons.
If you have a small pond, water garden or water feature then you may opt for a submersible pond filter that you can hide out of the way. These are great to filter the water if you are tight on space and some come with a built-in fountain head which looks cool.
If you are thinking about building a small pond filter then drop us a message and we will send you over the plans for ours. It’s really easy to build and only cost a few dollars to put together.