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We love our koi and we always want the best for them, right? Sometimes they can make it a little hard to love them. They’re the messiest eaters and, well, their biological output is prodigious, to say the least.
To keep your fish in tip-top condition you’ll need the best koi pond filter. In this article, I’ll tell you which filter gets my vote and we’ll see if there is any clear water between it and the rest.
Here are the koi pond filters we’ll look at:
- Grech CPF-2500 Pond Bio Pressure Filter **Top Choice**
- TetraPond 26596 Waterfall Filter
- CNZ All-in-One Pond Filter System
- OASE BioSmart 5000 Pond Filter
- Pennington Aquagarden Inpond 5 in 1 Pond Pump and Filter
Why Filters Matter in Koi Ponds
As we all know, koi are notoriously messy fish. Bottom feeders by nature, koi really enjoy grubbing about in the mud and silt that accumulates at the bottom of even the best-kept ponds. Even the best koi food sometimes doesn’t get eaten and ends up on the bottom. On top of this, the fish compound the problem with solid as well as ‘invisible’ waste.
At home, our filter needs to deal with algae in the water too because algae really love the bio-waste koi produce. We also have leaf fall and other materials that naturally end up in the pond over time, adding to the party. We’ve noticed that with koi being koi, and in an outside pond, the filter system is not only necessary but really does have its work cut out for it.
All koi are descended from a small group of fish in Niigata, where breeding started in earnest in the 1700s. Koi were selected and mated for their colors and patterns. The problem with this lack of biodiversity and inbreeding is that koi are generally less hardy than wild fish.
As a result, koi can suffer disproportionately in poor quality water. While koi fish live for a long time, poor water quality can reduce this lifespan. For koi specifically, the filter is the most important part of your pond system.
My Picks for Best Koi Pond Filter
Now that we’ve looked at the things you should know when choosing a filter, let’s take a look at my choices for best koi pond filter:
The first thing I noticed about this guy, right out of the box, was how large it was. It really was a nice surprise! The system is a waterfall (aerating device) and a filter all in one, which is quite a nice touch.
Designing functionality into a decorative piece is a masterstroke if you ask me. Just bear in mind the unit is a simple filter, so you will need a pump and UV light too.
It is essentially a large plastic, heavy-duty bucket with a robust lip for the waterfall. Installation is quick and easy, although a word of caution: the standard .75-inch garden hose will not fit. You will need either 1-inch or 1.25-inch tubing to complete the circuit with the pond.
The fitting was also quite difficult, so extra care should be taken when attaching the pump and checking for leaks. Note that the inlet is at the back of the unit rather than the side.
The filter did ship with filter pads, so mechanical filtration was great, right out of the box. There was no provision for biological filtration. Either lava rocks or bio-balls, whichever you prefer, will have to be bought separately. This was a small peeve on my behalf, as it was working well straight out of the box with no complicated set-up.
A small side note to Tetra: can you please make the stickers easier to remove? The stickers on the sides of the filter were next to impossible to remove and really didn’t add to the look at all. This is only a cosmetic gripe, I know, but it looks a bit unsightly.
- Simple, basic, and effective
- Works right from the box, easy installation
- Great price
- Added as a water feature, enhances the pond’s aesthetics
- The waterfall can aid with aeration
- Non-standard hose fitting which needs to be bought separately
- No biofilter material was provided, this seems like an oversight
- Inlet at the back, made plumbing in harder than it needed to be
This is the second of the single-purpose pond filters, a simple self-contained filter unit with no pump. The design is basic but well thought out. It is large, but not too huge that it can’t be concealed in or behind an ornamental feature.
Like the Tetra, the Grech is another easy, plug-in-and-run system. I think you get more bang for your buck here with both mechanical and biological filtration systems ready to go and a UV filter, you really do get the best of all worlds.
The bit that I liked best was the super simple backflush system. By reversing the flow of the water (flushing out collected debris) and turning the handle on top for five minutes I could easily clean the filter. It was super quick, no fuss, no stress and best of all, no mess. Compared to some other systems, this one is a breeze to clean.
- The super-easy cleaning system
- Biological and mechanical filters ready to go out of the box
- Excellent value for the features
- UV filter
- Some users report leaking issues
CNZ’s offering is an in-water, all-in-one system with mechanical, biological, and UV functionality. The built-in pump has a fountainhead attachment for ornamental use and additional aeration.
This is a great filter for a smaller pond or an additional filter in a much larger pond or series of ponds. Installation is easy; put the filter system in the pond and switch it on. Nothing could be simpler. The unit comes with 15 meters of sealed cable to help reach the more remote areas of a garden.
The filter itself is a single box unit. Access to the filter chambers for maintenance and cleaning is via two clips located on either side of the filter box. Here I did find a minor niggle as the mechanical filters can be messy when cleaning and removing them from the machine.
Note that the machine is heavy when waterlogged and removing it from the pond can be quite an exercise all by itself. There is no handle on the casing so if it is wet, slimy, and covered in algae, it can be a two-person job.
The fountainhead out has a splitter valve that can divert some or all of the water to a separate water feature. As an additional bonus, this sets the CNZ apart from quite a few other models on the market.
- Biological, mechanical, and UV filtration
- Great value for money
- Built-in pump
- Fountain and water feature
- Unit heavy to lift out of water when full
- Cleaning the foam filters is messy without backwash capability
This is the largest capacity and also the most expensive filter on our list. It is a stand-alone unit with a gravity-assisted feed out, so it needs to be situated a bit higher than the pool. It isn’t small, so concealment will take a little extra thought.
The OASE is a filter-only unit, so you will need a pump with an appropriate throughput. I found that the filter struggled with the higher flow rate of my larger pump.
One slight annoyance is the outlet: there is no connector or hose supplied and as it’s a non-standard size, a trip to the hardware store was in order. Not quite the plug-in-and-go style of others reviewed.
Features unique to this model included temperature and pop-up cleaning indicators, to allow you to keep the pump working at maximum efficiency. Cleaning was pretty easy. Six or seven minutes on the backflow setting and all was flowing smoothly again.
- Ease of cleaning
- Good filtration
- Cleaning Indicator
- Temperature Indicator
- Terrible instruction manual, just arrows pointing at various unlabeled parts
- Poorly designed outflow nozzle and fitting
The last of my reviews is this in-water combination system by Pennington. Like other units reviewed, it’s another plug-in-and-play system that is simplicity exemplified—five minutes out of the box and it was in my pond and working.
This is certainly a filter system for smaller ponds but despite the size, it has a few tricks up its sleeve. Dual biological and mechanical filters offer flexibility and the UV option helps with algae. It has a fountain with three head attachments and an optional water feature.
Pennington’s unit also has an LED light so you can bring a bit of glamour to the evenings and show off your fish whenever your guests come round.
Cleaning the filters is easy. The unit’s smaller size makes it easy to remove, clean, and replace parts if needed. One downside is the two plugs, one for the UV and light and one for the pump. It isn’t a big gripe, but having two outlets by the pond is an extra bind and could have been avoided easily.
- Works straight out of the box
- Small, sturdy, and compact
- LED light an extra bonus
- Two outlets needed
- The fountain has no splitter for extra water feature
Best Koi Pond Filter: The Verdict
From the outset, I wanted to say there was a clear winner in our quest for clean water and I’m pleased to report that overall, there is. The Grech CPF did everything that was asked of it and more. Furthermore, this unit did so for a great price and with a 1600 GA rating—certainly no slouch in the ‘size matters’ category.
The ease of installation, pretty much plug-in-and-go (once the connectivity issues are sorted out), and ease of cleaning made this a winner in my book. Grech beats out the slightly cheaper Tetrapond by virtue of having UV and the biological substrate included.
All in all, for the price, capacity, ease of use and completeness, this really is the best koi pond filter to get the job done. After two days, the water quality in my koi pond was looking great. A recommended purchase for any small to medium koi pond.
What to Look for in a Koi Pond Filter
Let’s cover the basics first: cost. To put it simply, buy the very best koi pond filtration system you can. You probably have a budget for your pond and I think the key purchase you’ll make is the filter.
As a koi carp rule of thumb, bigger is always better when it comes to filters. Your koi will grow into their pond and this growth means their waste output will increase too. You need to account for this year after year.
Size matters aside, here are a few other things you’ll want to consider:
Mechanical Versus Biological Filtration
A mechanical filter physically separates particulates from the water by barriers, screens, beads, mats or a combination of these. They can remove leaves, bits of twigs, and bio-waste from the koi. Mechanical filters are also capable of clearing the water of small suspended particulates, mere fractions of a millimeter across.
Mechanical filtration will clean your ponds and make them look nice and pristine. Your crystal clear water will be the envy of everyone in the neighborhood. This isn’t the whole story, however, and clear water isn’t necessarily clean water.
Biological filtration is the second source of water health to consider. We have already talked about how messy koi are at the dining table, now we need to talk about their bathroom habits.
The bio-waste they produce is beloved by many, many bugs, and this is the problem. Although you can’t see them, they will certainly have a huge impact on water quality and fish health.
Biological filters have different substrates present that encourage and promote the growth of good bacteria. These bacteria, when the water flows over them, will feed on the ammonia in the water, converting it into the benign Nitrate.
There is a range of different substrates on out there but each, essentially, does the same thing. The main aim is to have a large surface area for the good bacteria to grow on while having enough space to allow the water to flow through the substrate.
UV lights are used to make the algae clump together. These larger masses are much easier to catch and filter out than the single cells themselves. Some filters and filtration systems have integrated UV filters and others need a separate system.
Both are effective and each has merits and flaws. Having a single until means less cabling and less connections but having a single combined unit may mean it’s harder to access, clean, or replace parts.
How Big is Big Enough?
We know our koi like to dine on the bottom and we know this kicks up silt, mud, and all sorts of biological mess. How do we account for this then?
Start with the size of your pond. The standard formula for the volume:
Length x Breadth x Depth
With koi, we have to multiply this by a factor of four to get the volume needed for the water exchange value of the pump. Koi are four times messier than your average pond fish.
If you have a pool volume of 1000 gallons and pumps with a flow rate of 900 GA and 1200 GA, I would always upsize. As I said earlier, bigger is always better!
We have to match the filter to the pump. Too much capacity in the pump and you might flood the filter, not enough and the filter isn’t effective and your pond will get dirtier and dirtier. A good maxim to cycle the water of your pond every hour. A 1,000 GA pond would benefit from a pump with a throughput rate of 1,000 GA per hour.
You should remember though, that if the filter box is above the level of the pond the pump, the pumping against gravity and will have to work harder. If that’s the case with your system, factor in a little extra capacity.
FIlters need pumps and pumps need power. Don’t forget that all cabling needs to be weatherproofed and waterproofed (where necessary). Think about ease of access to the electrics, both when laying and for maintenance.
The very nature of filters means they are going to get dirty. Part of your koi care routine involves cleaning the filter on a regular basis. It’s important to follow the manufacturer’s instructions and not to take any shortcuts here.
It isn’t the most pleasant of tasks, let’s be honest, so it really is worthwhile getting a filter box or system that’s easy to clean, disassemble, and replace parts. There is nothing worse than putting off that nasty job for a day or two when it’s cold and wet because, at the end of the day, it’s the quality of the water that will suffer.
A good koi pond filter is essential to have the best koi pond possible. Your water will not only look better but your koi will thank you as well!