OC-1 Filter Media in a Domestic Swimming Pool - The Review

How is OC-1 performing so far?


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 seasonal domestic
Pump Certikin Swimflo HPS031M Flow rate at 10 mtr head 8 cu mtr hr
Filter Certikin ZZOC-1/20 Filter Diameter 20"

At Last:


After a delay from a tremendous thunderstorm in the afternoon, at 17.00 hrs on Tuesday 16th June 2000, at least a month behind schedule, the multiport valve was set to waste, the pump was primed as best I could, and turned on. The initial priming took a long tme, worryingly so, but eventually full flow was achieved. After a few minutes to waste, the valve was switched to filter and the air valve on the filter opened. The filter filled, and settled down to a low pressure of just under 0.5 bar, or 6 or 7 psi, rising slightly during the evening. The normal pressure at the start of a filtering cycle is, according to the brochure, 0.8 kg/cm² or 11.4 psi (but the gauge is in bar, which is as near as dammit to kg/cm²). The OC-1, or some of it, rose up to the filter lid and stayed there, these particules will drop, I trust, over the coming days.

Right from the start the first objective was achieved. No filter media is ever going to get into the pool.

The pool water is not unattractive, mostly blue but rather murky, presumably due to dead algae and dissolved solids. It is possible to make out the head of the brush in the shallow end (750 mm) but only just. The pool hasn't been used for almost two years, so I dread to think what is lying on the floor at the deep end. The pump was left running continuously with both low suction and the skimmer open.

Filter Pressure at startup 16/06/20

Brush head just visible in 750 mm water 16/06/20


Pressure still at 7 psi, and the water still cloudy. The OC-1 has fallen back from the filter lid, and the top laterals can be seen working. The flow seems quite feeble, but there are a lot of slots in the laterals, 80 in total, to take the flow.

Whilst waiting for the system to settle in, what exactly is a flow of 5 m³/hr? ABS 1.5" pipe has an internal diameter of 42 mm whch gives an area of 1,385 mm². One metre of pipework therefore holds 1,385,000 mm³, which sounds a lot but is actually 1.385 litres. Coincidentally 1.385 litres a second is 5 m³/hr, so the desired flow through the pipework is one metre per second. After all that I still don't know if I am getting 1.385 litres a second, the return to the pool certainly seems powerful enough to provide this.

I had expected the flow in the filter to be strong, but it isn't. However even at a high flow rate, say 12 m³/hr, that is 200 litres a minute, 3.33 litres a second. There are 80 slots in the laterals, so each slot emits 42 millilitres a second, which isn't much (and the flow probably is less than 12 m³/hr).


Everything grinds to a halt. The pool water is cloudy, after all the pool hasn't been used or maintained for getting on for two years, and I can't get it to clear. The pump is pulling 650 watts, is blisteringly hot, and using about £20 of electricity a week. It is a 0.5 HP pump, not a 0.3 HP. It is also making some funny noises. After a great deal of effort I finally hit upon a comment in a USA forum that the power demand of a centrifugal pump is proportional to the head times the flow rate. The flow at the return certainly seems very powerful, but I don't have a flow meter. I have found another reference that says that when the pump is at the low head/high flow rate end of the flow/head chart it is at its highest power consumption. I made a lot of effort to reduce the friction in the system and now the pump is suicidal. I think that the high flow rate, which may well be around 60 m³/m²/hr, is too fast for the OC-1 to cope. I shall contact the suppliers to expedite a swap.

Certikin Tech devision have been helpful in this, but can't explain the pump labelling. They have contacted the manufacturer in Spain for an explanation.


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