If you’ve been following my breeding project here on Nishikigoi.Life, or on my YouTube channel, you’ll possibly remember that after the initial spawning efforts and questionably successful spawning on 18th May, a temporary 2700 litre Intex paddling pool was set up to separate males and females to prevent accidental in pond spawning taking place, should a second spawning be needed.

2700 litre Intex pool

2700 litre Intex pool

This pool was only ever intended to be a very temporary installation, however that has somewhat changed now…….

In its temporary guise it was clearly going to need some kind of simple biological filtration to take the edge off of likely ammonia and nitrite build ups, without resorting to excessive and constant water changes, and also enabling at least a little food to be given.

The first idea enclosed around 20 litres of mature K1 from the Nexus and a flat airstone inside 2 large water plant baskets.  With some perseverance it would probably have worked, indeed smaller baskets keeping it all submerged may have worked better, but it felt that there wasn’t enough water exchange.

A trip to Manor Koi procured a black bucket and some bits of pipe to manufacturer a simple bubble up filter, taking me right back to my very first goldfish aquarium nearly 40 years ago, where this whole hobby started for me.  Air driven filters were very much the norm then, whether little plastic boxes, or under gravel filters.  The concept is simple, air is pumped into the box, as it exits it takes water with it, gravity then causes water to enter the box to fill the void, as doing so passing over/through the filter media.

Original 'bucket' airlift filter

Original ‘bucket’ airlift filter

The first bucket was filled with K1 again, however it became apparent that some ballast was required to stop it floating around.  A message to my nephew who works at Manor Koi saw him dropping off a bag of Alfagrog on his way home.


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I’m not entirely sure when Alfagrog came onto the market as a filter media, what I do know is that other than knowing its name, it had never entered my consciousness as something i’d use, in fact if you’d suggested it I would have run a mile screaming.

Bag of Alfagrog

Bag of Alfagrog

So why would Alfagrog filled me with such dread?  I suppose it’s because historically ‘stone’ media have come with all manner of potential problems; they are heavy, block easily, relatively low surface area compared to plastic media, difficult to handle, the list goes on.

Upon opening the bag of Alfagrog, which I’d purchased simply for its weight really, i was struck by a media which was nothing like I’d expected.

Firstly it was far lighter than anticipated, so much so that around 12cm of it in the bottom of the black bucket really didn’t weigh it down on the bottom as anticipated.  Only later with all the K1 plastic media removed did the bucket sit firm, although it was still by no means heavy.  A single bag weighs 15kg and has a volume of around 20 litres.

Secondly was the obvious surface area that the media had.  Apparently Alfagrog comes in 2 standard sizes, E25 and E40, the number relating to the particle size, i.e. 25mm or 40mm, although the pieces are far from being regular sized and shaped balls.  The Alfagrog I have is E40, and whilst this may have a smaller surface area than the E25, I would suggest that it is unlikely to pack down as much in the filter.  According to the Alfagrog website the E40 has a Specific Surface Area of 45m² per litre (the E25 has 90m²).

Close up of Alfagrog

Close up of Alfagrog

At that stage, before even using it, I was just a little surprised why I’d never even looked at Alfagrog, and to the best of my memory never actually ever touched it.


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Aided by an EA Pure Pond Bomb, which went inside the bucket, and nominal water changes, the bucket filter soon had the parameters under control in the Intex pool.

Indeed, a short while later I wrote on Facebook:

‘A sight to make some run for the hills or cry out in pain…………

I have to be honest I’ve always considered Alfagrog something to be kept at arms distance, despite never actually using it nor I think even touching it, literally never touching it.

However, 10 or 11 days ago I got a bag as I needed some ballast to weigh down my bucket filter in my temporary Intex pool.

Ever since I’ve developed a bit of a thing for it. It’s doing a great job in the Intex pool, in fact I’m just making a second bucket to run in there to establish it for when the babies move outside.


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I’m not sure why anyone would dismiss Alfagrog in preference of BHM or any other ceramic media in showers or in submerged filters to be honest. It weighs much less than I’d expected and clearly has a massive surface area.’

Zero ammonia, 24th June

Zero ammonia, 24th June

As it became increasingly apparent the Intex pool was likely to have a longer life than its originally intended temporary tenure I started to think about how I could filter it on a more permanent basis.

A couple of things that have become obvious to me in this short period of breeding are the value of quality water, in that I mean access to quality water, and the need for robust biological filtration, filtration that can adapt quickly to changes in pollutant levels.  It’s long been suggested that natural media excel in this department compared to plastic media.

When I built the Koi house here over winter there was a point when it became clear there were lots of points about it that were ‘nice to haves’ and not ‘need to haves’.  Many a time I would say to people, ‘the simple farmer wouldn’t have bothered with that!’.  For anyone that has visited Yoshikigoi in Poland they’ll be aware that even given the size of the farm, many aspects are not showy, or fancy, whatever was at hand to be made to fulfil the job was used in respect of some holding tanks and filters.  My visit to Fabio at Koi Lab in Italy – http://nishikigoi.life/2019/05/03/a-visit-to-koi-lab-italy-part-1/ – was a revelation to me in the fact of how effectively Intex pools could be used, indeed i ended that report with; ‘I can’t help but keep wonder where i can find space to fit 6 large collapsible swimming pools………’.  Realistically, in terms of cost per litre of water, I doubt there is anything cheaper than the Intex type swimming pools.

I joked the other day on Facebook about ordering the new Koi house for ‘Gardner Koi Farm’ and posted the picture below.

Not my new Koi house

Not my new Koi house

Of course, that’s not the reality, and neither would some state of the art breeding facility be decked out with drums or nexus or showers or whatever other options exist.


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The prime objective of all that has been done with the breeding this year (now extending to 3 spawning) is to learn, what works, what doesn’t, and there has been plenty to learn that’s for sure.

So, with one Intex pool in situ, and needing a filtration system to go on it – and something that potentially could easily be scaled at reasonable cost in the future – project ‘⍺-Stream’ was born.  (note ⍺ as in alpha, alpha stream, a play on alfagrog).  Of course, I’m very aware that this is not exactly ground breaking stuff, there are thousands of filters around the UK and beyond that contain Alfagrog in one way, shape or form I am sure.  Sadly i fear many of those filters ‘thrive’ on neglect, are clogged with muck, and poor old Alfagrog gets a bad name.

Anyway, first off I needed a ‘container’ into which the ‘⍺-Stream’ could be built.  I didn’t need to look much further than just down the road at Manor Koi where for over 25 years they’ve been manufacturing their own fibreglass multi chamber filtration systems, as you can see from the July 1995 Koi Carp magazine advert below.  (The address and phone number remain the same 24 years on, should you want to visit or contact them).

Manor Koi advert in Koi Carp July 1995

Manor Koi advert in Koi Carp July 1995

I didn’t actually want a multi chamber design, just a single chamber, and discussing it with Martin Green it was possible to manufacture a custom model of the unit that is in the advert without up/down transfer ports, just as I wanted.  I also added a small vortex to the front of it, not that it will be used as a vortex, but customised to include a static K1 chamber, similar to the Nexus and EazyPod, which do a great job of removing solid waste.  You can find a diagram of such a system on the Cuttlebrook Koi Farm website – http://cuttlebrookkoifarm.co.uk/cuttlebrook-filtration/.  That however is a job for the future.

One criteria was that the Alfagrog needed to be easy to handle, and easy to remove to be cleaned if necessary.  Eight 40cm x 30cm x 10cm mushroom trays proved a pretty good fit, stacked 2 high and 4 long when placed side by side.  In an ideal world the trays would be 50cm x 30cm to fill the space better and fit a little more media in.  When 2 trays are stacked on top of one another there is an empty space of around 2cm between the upper and lower trays.  With aeration placed beneath the lower basket air rises freely through the media circulating water with it.  At present there are around 4 bags of Alfagrog in the filter giving a surface are of approximately 3600m².

1 of 8 baskets containing Alfagrog

1 of 8 baskets containing Alfagrog

air stones under each 'stack' of baskets moving water

air stones under each ‘stack’ of baskets moving water

Underwater shot showing column of bubbles passing' through media

Underwater shot showing column of bubbles passing’ through media

One  of 2 floating rafts of salad vegetables has been installed as well, the vegetables growing aquaponically taking their nutrients from the water.


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Floating tray of aquaponic greens

Floating tray of aquaponic greens

Two resources which we are constantly being encouraged to use less of are water and electricity.  It’s fair to say that Koi keepers generally use more than their fair share of each, especially with the use of RO water and drum filters which are constantly flushing waste water away in their clean cycles.

I was surprised by the amount of water that was moved in the bubble up bucket filters by very little air and was keen to use an airlift system on the ‘⍺-Stream’.  The potential for cost savings in the future are enormous, indeed with the system running on a 20lpm air pump using just 15w of power – moving water and aerating it at the same time.

Airlift 'pump' pipework

Airlift ‘pump’ pipework

The system has been set up just a few days and is guardian to the offspring from the final spawning of the season.  No doubt it will require tweaks along the way, particularly to the airlift for which there are probably many ways to make it more effective in the volume of water it moves.

I still need to find somewhere to fit 6 Intex pools…


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