A Guide to the Evolution Aqua Nexus EAZY 220+ and 320+

Evolution Aqua’s Nexus Pond Filtration Systems are high-quality items that we highly recommend here at Complete Koi & Aquatics. In particular, the Nexus EAZY 220+ and 320+ filtration systems are great products that will ensure that your Koi are both happy and healthy.

What is the Nexus EAZY 220/320+?

The Nexus range includes a set of pond filtration systems manufactured in the UK by the award-winning pond company, Evolution Aqua. Nexus filters are innovative, all-in-one biological and mechanical filtration systems designed specifically with Koi ponds in mind. The range consists of: 


Nexus 220+ – For Koi ponds up to 18,000 litres

Nexus 320+ – For Koi ponds up to 34,000 litres

The Nexus 220+ & 320+ are almost identical in construction however, the Nexus 320 is a slightly taller and wider unit and thus has a larger capacity for both media and water. In terms of design, the Nexus units are fairly simple. They consist of a central cage, known as an Eazy filter, situated within the Nexus inner chamber. This is filled with mechanical K1 micro media.

The outer chamber is fluidised to create a moving bed (i.e. air pumped through the water to enrich oxygen and create turbulence) and is filled with the all-new K+ media (which has replaced its predecessor K1 media), acting as biological filtration.

In terms of inlets and outlets, the Nexus has an inlet moving water from the pond into the filter's inner chamber and an outlet situated in the outer exit chamber, returning water to the pond. It also has two small ball valves which allow the draining of both the inner and outer chambers to waste. 

Mechanical and Biological filtration system

Mechanical filtration describes the process of removing solids and particles from water as it moves through a filtration system, resulting in cleaner water with higher clarity.

Biological filtration refers to the process by which beneficial bacteria, Nitrobacter & Nitrosomonas, consumes and removes Ammonia and Nitrite produced from fish waste, which is toxic to aquatic life. This is an incredibly important process within a pond.

What do the Nexus 220 and 320 do?

Nexus filtration systems use two different media, which are similar in appearance but differ greatly in size.

Each media plays a unique role within the filter:

K1 Micro

K1 Micro is the first of these. This is found within the inner chamber of the Nexus. As the name suggests, K1 is a small media which holds two purposes, the first being mechanical filtration. Mechanical filtration is the removal of pond solids and fish waste from water. In this instance, pond water is forced through a central cage (known as the Eazy filter) of tightly packed, static K1 micro media which collects and holds any solids too large to pass through the gaps.

The second purpose of K1 micro media is in biological filtration. K1 micro is a highly engineered product with a particularly large surface area of 1,400m2 per m3. This makes it a great home for good pond bacteria such as Nitrobacter and Nitrosomonas. These bacteria consume ammonia (NH3) and nitrite (NO2) which are both by-products of fish waste.


Coincidentally, Ammonia and Nitrite are toxic to aquatic life, fish in particular, so the biological role of K1 micro is incredibly important. You can buy K1 Micro media here.

K1+ Media

K+ media is the big brother of K1 micro, with an overall surface area of 1,350m2 per m3. K+ is larger in size and purely acts as biological filtration. K+ lives in the outer chamber of the Nexus which is aerated to create a moving bed. This enriches the water with oxygen causing the bacterial colonies to thrive, thereby dramatically increasing the biological efficiency of the filter.

The turbulence created in the moving bed also knocks any escaped solids off of the media, maintaining a clean environment for the bacteria to colonise. Good biological filtration is essential when keeping higher stocks of large fish, such as what is commonly seen in Koi ponds. 

The previous model of Nexus contained K1 media as a predecessor to K+ media. This media was fantastic for its time, having a large surface area of 950m2 per m3. K1 is still readily available here and makes a fantastic addition as a biological media in any situation.  

What do the Nexus EAZY 220+ and 320+ feature?

The product is well thought out, featuring fantastic levels of both mechanical and biological filtration- thanks to the highly engineered K1 media. On top of this, the Nexus can easily be paired up with additional mechanical and/or biological filtration, such as a bead filters and sieves (Cetus sieves, for example). The possibilities really are endless.

The Nexus’ are extremely robust in build- they are constructed from plastic on a rotation-moulding machine. This plastic is also reinforced with beads, which you can see in the mottled finish of the Nexus. This further reinforces the casing. As a result, they are not likely to get damaged or be affected by cold weather. They really are, almost indestructible. 

In terms of size, the footprint of the Nexus may seem large, but it is actually very compact based on the performance. To put it simply, a bay filter delivering similar amounts of filtration would typically be over 8ft+ long. The Nexus, at its widest point, is a little over 4ft!

Besides this, anyone who has ever owned a bay filter will know how arduous cleaning can be. With bay filters, you have to strip down every component part and clean accordingly. This is not only time consuming, but very smelly and messy. One of our old customers used to say the greatest thing about the Nexus- “I can clean it in my Sunday best!”. Essentially, the Nexus is very simple and hassle free to clean. 

Specifications of the Nexus 220+ and 320+

What is the difference between the Nexus 220+ and 320+?

The main differences between the Nexus 220+ and 320+ are the specifications listed below. The 320+ is more expensive as it has a larger capacity, volume and flow rate.

Nexus 220+

  • Pond size – 18,000 litres
  • Flow rate – 10,000 litres per hour
  • Media Capacity – 150 litres 
  • Volume – 510 litres
  • Dimensions - (L) 1260mm X (W) 1110mm X (H) 850mm 

Nexus 320+

  • Pond size – 34,000 litres
  • Flow rate – 13,000 litres per hour
  • Media Capacity – 300 litres
  • Volume - 840 litres
  • Dimensions – (L) 1430mm X (W) 1320mm X (H) 1025mm 

As mentioned previously, the Nexus’ are rated to the following pond sizes:

Nexus 220+ – For Koi ponds up to 18,000 litres

Nexus 320+ – For Koi pond up to 34,000 litres

It is worth mentioning at this point, when it comes to filtration, that there is no such thing as over filtering. More really is, more. We advise getting the biggest filtration system you can fit or afford. The bigger you go, the clearer your water and the higher level of fish stock you can have.

How do the Nexus 220 and 320 work?

Mechanical filtration stage

Water enters the filter from the pond via the inlet, which is connected to the inner chamber of the Nexus. The inner chamber forces water to vortex around the Eazy filter, which is a cage containing K1 micro media. This action causes any large solids in the water to settle at the bottom of the inner chamber. The water then moves through the Eazy filter and the K1 micro media, which removes finer solids and particles present in the water.

Biological treatment and breakdown

Once the water is largely absent of solids (which are held up in the Eazy filter containing K1 micro media), it then passes through the centre of the Nexus where it is distributed into the outer chamber. This Nexus chamber is aerated (known as a moving bed) and contains K1/K+ media. This stage is designed to biologically treat the water passing through the outer chamber prior to being returned to the pond. 

Water in contact with the media undergoes a biological breakdown whereby bacterium, Nitrobacter and Nitrosomonas living on the media, consumes Ammonia (NH3) and Nitrite (NO2) present in the water as a by-product of fish waste. The bacteria convert the harmful compounds into a less harmful dissolved gas, nitrate (NO3), which naturally leaves the filter. 

The water has now been treated and is ready to be returned to your Koi Carp. From here, the water enters the exit grill; dropping down the outlet where it is returned to the pond. 


How to install the Nexus EAZY 220+ and 320+

To begin with, it is important to note that the Nexus+ MUST be installed on a solid, level base; a minimum of 1.2 metres x 1 metre. Failure to do this can cause irreparable damage to the filter and will therefore invalidate your warranty.

When installing a filtration system, there are two possible options- Gravity-fed and Pump-fed, which we will further discuss below:



By this, we mean that your pump is going to be used to return the filtered water to the pond and therefore, your filter will be supplied by gravity via a larger diameter pipe. In this situation the water level in the filter will be at the same level as the pond.

The diagram below clearly demonstrates a Gravity-fed system:


If your pump is going to be used to supply the water to the filter, and the filtered water then returns back into your pond via gravity, i.e. down a waterfall or through a large diameter pipe, this is referred to as pump-fed. Basically, the water is fed to the filter using a pump.

The diagram below clearly demonstrates a Pump-fed system:

How are the Nexus 220+ and 320+ different to other filtration systems?

As mentioned previously, the brilliance of the Nexus is in its simplicity. It doesn’t actually have many of the features other pond filters have, but this is what makes it so good. The Nexus range really is unique when it comes to pond filtration.

Take a pressure filter as an example, which normally comes with a cleaning mechanism such as pump/turn handles. This requires the owner to engage a cleaning valve, diverting the water to waste, whilst manually disturbing the filter sponges/media. This can often be tiring work and it is unlikely that the filter will ever be truly clean. In the Nexus, the cleaning is undertaken by simply altering an air valve to disturb the K1 micro media. No hard or messy work is required. 

It also doesn’t come with a UV, as many pressure and box filters do; this may sound like a disadvantage, but it is actually a great move by Evolution Aqua. UV is what gives you ultimate water clarity, particularly in summer when algae is thriving. When using a filter which comes with pre-determined, built in UV, you are dictated by the size of that particular UV unit. The Nexus’ are modular and can therefore have any size UV! We always suggest getting the largest UV unit you can fit or afford. Anything is possible with Nexus. 

As mentioned previously, the greatest accolade of the Nexus has got to be its highly-engineered pond media. It is unrivalled when it comes to biological filtration, offering extremely high performance for your beloved Koi carp. 


Main benefit of the Nexus EAZY 220/320+

Compared with the previous model of Nexus, the main improvement in the 220/320+ is in the media, as discussed in previous paragraphs. K+ is now the standard media in all Nexus, offering enhanced biological filtration. The result? Far better water quality and happy Koi.

Why do I need a Nexus pond filtration system?

Evolution Aqua have developed a sophisticated product in the Nexus, which is both simple and effective. The Nexus has no moving parts and as a result, is unlikely to fail. Compare this with a drum filter or similar filters which are automated to self-clean when required; they are great in principle however, when they fail they can cause catastrophic issues within a pond which can be expensive to fix.

A Nexus owner needs to understand the importance of routinely conducting preventative maintenance on a Koi pond, whilst checking the fish and pond itself for any potential issues. This is also a great time to clean your Nexus, giving the pond that ALL important, gin-clear water!


How do I clean the Nexus 220/320+?

Cleaning a Nexus filter is a very simple process, often accompanied by a nice mug of tea or coffee:

  1. To begin with, turn the pump off that is feeding your filter/pond.

  2. Isolate the filter by closing any valves to stop water moving in or out of the filter.

  3. Insert the cleaning pipe into the centre of the Nexus, stopping water moving between the inner and outer chamber.

  4. Turn on the valve directing air to the inner chamber cage, which will agitate the water creating turbulence in the K1 micro media cage- this will dislodge any solid waste held by the K1 micro into the inner chamber. This needs to be done for several minutes to properly cleanse the K1 of fish waste. Now is a great time to enjoy your mug of tea or coffee and admire your Koi carp!

  5. Once the K1 micro has been bubbling for several minutes, it is time to open the waste valve for the inner chamber. This will send all of the soiled water and solid particles out of the Nexus to waste.

  6. Once the inner chamber has emptied, close the waste valve and switch the air valve back to the Nexus outer chamber.
  7. Refill the inner chamber of the Nexus by opening the relevant valves, connecting the filter to the pond and removing the Nexus cleaning pipe, allowing water to circulate between the inner and outer chamber once again.
  8. Turn the pump back on, recirculating water between the pond and filter.
  9. Top up the filter/pond to the required level.

How long do the Nexus 220 and 320+ last?

As mentioned previously, the Nexus’ are pretty much indestructible. They are of extremely high-build quality and as a result, should last the test of time regardless of what the weather throws at it.

Do they have any warranty?

They come with a standard 1-year manufacturer’s warranty however, we highly doubt you will ever have to use this. 

What products should I use with the Nexus 220/320?

In terms of products which can be paired with the Nexus, the world is your oyster given the modular nature of the system.

Here are some of our favourite pairings: 

Pipe work-

Pipework is obviously an essential part of having a pond. In terms of pipework, all of the Evolution Aqua pressure pipe fittings are of fantastic quality and can be viewed here.

You are likely to require the following bits of kit:


When it comes to pumps used in conjunction with the Nexus, we prefer to use the following:

  • Hailea Pumps by Charles Austen are of outstanding quality, delivering incredibly consistent performance. They can be used both wet and dry mounted (i.e. in the water or out of the water) and come in a variety of sizes to suit almost any situation. Best of all, they are great value for money.

  • Varipumps by Evolution Aqua are another fantastic option when it comes to pond pumps. This is a controllable pond pump, available in 3 sizes. Output and energy can be controlled at the push of a button, allowing the user to adjust flow rates to suit and save money on energy when lower flow is required (i.e. in winter).


UV lights are of paramount importance in a Koi pond, delivering gin-clear water for the ultimate viewing experience. We always say when it comes to UV, go as big as you can fit or afford.

We especially like the following UV products:

  • Kockney Koi is the largest independent manufacturer of Koi Pond products in the UK. They have years of experience and create some truly excellent, great value products. Their UV lights are discreet and powerful and are highly recommended.

  • Evolution Aqua manufactures a fantastic range of UV products known as the EVO range. They are well built, manufactured in the UK and deliver high performance at great value. 

Air Pumps-

When it comes to air pumps, we firmly stand behind Charles Austen as a manufacturer. Charles Austen were established in the 1940’s, manufacturing exceptionally high-quality pumps of all varieties for just about any situation. They really are masters in their field and make bomb-proof air pumps, which are fantastic for Koi ponds. 

Additional Filtration-

As mentioned previously, the Nexus can be paired with additional biological/mechanical filtration to create a true masterpiece.

Our favourite examples of this are as follows: 

  • Cetus Sieves are pre-filters with bow screens, designed to remove large amounts of mechanical waste before it enters the next stage of filtration- in this case the Nexus. Solid waste consumes oxygen and releases ammonia and other compounds into the water. The Cetus Sieve therefore polishes the water, providing higher clarity and enhancing biological filtration in the Nexus.

  • Microbead Filters are pressurised filtration systems. The best examples of such filters are without doubt the K1 micro range by Evolution Aqua. Filled with K1 micro media, they offer fantastic levels of both mechanical and biological filtration, polishing the water and removing harmful compounds. When using with a Nexus they have to be pressurised, so will always be between the pump and the Nexus depending on whether the system is pump-fed or gravity-fed.

Biological Additives/Enhancers-

When establishing a new pond and thus, a new filter, biological additives are absolutely essential. They also play a role in maintaining biological filtration in a mature pond. You are looking after the water which will in-turn, keep your Koi Carp happy and healthy. In order to do this, you should feed and promote bacterial colonisation within the filter.

Our favourite products for doing this are as follows:

  • NT Labs Filter Bugs – NT Labs are a well-established aquatics business with a phenomenal reputation. They make exceptional pond additives/treatments and their filter bugs, liquid formulation of essential nitrifying bacteria, is a fantastic product to add to your Nexus.

  • Pure Pond / Pond Bombs – Much like the NT labs product, this is live bacteria used in both new systems and in pond upkeep/maintenance. These are black jelly-like balls filled with huge colonies of good bacteria which dissolve into your filter/pond.

Can I get spare parts for the Nexus 220 and 320?

All possible parts of a Nexus are available as spares should you require them. If you’re having an issue and require a replacement part, don’t hesitate to contact Complete Koi & Aquatics – 01204 582105 / info@completekoi.com
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