OC-1 Filter and Media in a Domestic Swimming Pool

Why I chose OC-1 filter media


Pool details

Pool size 15 mtr X 4.5 mtr Pool shape Rectangular with Roman steps
Pool type Delifol vinyl liner UK Situation Inground
Capacity 50 cu mtrs Use Occasional seanal domestic
Pump Certikin Swimflo HPS031M Flow rate at 10 mtr head 8 cu mtr hr
Filter Certikin ZZOC-1/20 Filter Diameter 20"


Why did I chose to go with OC-1 filter media instead of the ubiquitous and well-known options, or any of the many other common to more extreme alternatives? Part cost, part reason, part ease of use, part prejudice, part cantankerousness.

It's not easy going with OC-1. There's a dearth of publicity, support, usage, and information out there. You do feel that you are rather out on your own at times. In some cases OC-1, or any 'new' filter media is dismissed - perhaps with some justification - as snake oil. It's a punt in the dark, and you have to be stubborn, or gullible, or bloody-minded.

I narrowed the alternative filter types down to three, sand, cartridge, or diatomaceous earth.

Diatomaceous Earth:

Just too messy, and not popular in the UK. All that dubious powder, and filter cleaning, put me off.


A tempting choice, in size, filtering capability, and cost. They were perhaps a little too tall for my setup, and had no provision for pre-filtering, or either switching to or connecting a vacuum hose. These complications ruled them out, just.


Thee overwhelming choice for pools everywhere. They are well known, idiot-proof and perform reasonably well no matter how abused. The multiport valve does most things, and they are reasonably compact if rather expensive. So I chose a sand filter, but without the sand.


I looked (mainly on YouTube) at the many alternatives to sand, and dismissed all except one. Glass didn't seem to have any advantages over sand; foam balls, fluffy balls, etc. seemed to disintegrate or become filthy and I don't want to spend time with my arm stuck deep into a filter digging out stinking goo; and the Zeoclere (which Certikin sells) and other brands seemed too much like sludge.


OC-1 has its collection of amazing qualities, just as all the other media does, but some of them could be just a little more believable. What swung me was:

1) It is backed by Certikin, a major company

2) It will never, ever find its way into the pool

3) It seems more washable, or backwashable, than foam or fluff

4) Its open structure lowers resistance to flow

5) It requires no more maintenance than sand

6) It filters to one micron, so they say

7) It has favourable independent testing

8) It can't cake or clog or channel

So OC-1 it is.

The pieces of OC-1 are made out of hard blue HDPE plastic and are surprisingly small, approximately 9 mm in diameter with the little 'fins' on the outer edge taking the diameter up to 10 mm, and a depth of 7 mm.

OC-1 Filter Media

There are approximately 1,000,000 pieces of OC-1 in 1 m³ and each piece has 12 open cells. A 50 litre bag of OC-1 therefore holds approximately 50,000 pieces of OC-1, providing 600,000 individual cells for the settlement of debris.

The OC-1 20" filter comes with 70 litres of OC-1. There's no definitive quantity specified anywhere. Not on the filter, nor the OC-1 bags, and the OC-1 websites are notably lacking in this area. The mantra seems to be to divide the sand quantity in kg by 1.59 to give the OC-1 required in litres. Whilst this may help filter conversions it is useless when using the OC-1 filter. As it turned out 70 litres was just about right, coming up two thirds of the filter body to the top of the upper bulkhead fitting. A presentation circa 2015/16 by Certikin's Steve Nelson says that a 20" filter requires 50 Litres OC-1, but more media - up to a point - must contain more pieces and more filtration surface. Perhaps nobody really knows what the actual quantity should be, or perhaps it doesn't matter.

There's no information about anything reproduced anywhere on the bags of OC-1, just where it should be.

OC-1 can be used with a filtration rate from 10m³/m²/hr to 50m³/m²/hr 'and above'. For a 20" filter with a filter area of 0.18 m² that is a flow beween 1.8 and 9 m³/hr, which fits a smaller pump exactly. This compares to the optimum filtration flow rate of sand, which is as low as possible, and conficts with often oversized pumps.

The open nature of OC-1 means that the flow rate can 'increase compared to using sand' by 20%. I think this means that the resistance - the head - is lowered, enabling a less powerful pump to be used to obtain the same flow rate.

As a side note the use of Polyaluminium Chloride as a flocculant with OC-1 is forbidden, as - God forbid - is adding a handful of diatomaceous earth to the filter or any substance that creates a film on top of the media. Whether the use of any other flocculant is acceptable isn't known. However Certikin sells Swimfresh Ultimate Clarifier for use with OC-1, but only in commercial quantities and thus presumably for commercial installations only. There exists Swimfresh Clarifier but this is not specified as being suitable for use with OC-1. It appears to be produced by CPC Pools as an own-label cationic clarifier, so nothing too special or peculiar to OC-1. Why a clarifier is required with OC-1 if it filters down to one micron is not exactly clear.


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