Changing from sand to glass media filtration

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COYS
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Post by COYS »

RichardHenshall wrote:Surely improved suction equates to reduced filtration. It may make lifting larger leaves etc easier but the finer particles will initially just go straight through the filter. It's the build-up of finer particles that improves filtration.
Quite possibly RH, however I always fish out any larger stuff first. We are seasonally prone to weather borne red dust that settles at the bottom & it is this that I've found is vacced up far more efficiently since the sand change. As said, only a guess that it's relative but long may it continue or at least until the dust has abated.
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teapot
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Post by teapot »

COYS wrote:
RichardHenshall wrote:Surely improved suction equates to reduced filtration. It may make lifting larger leaves etc easier but the finer particles will initially just go straight through the filter. It's the build-up of finer particles that improves filtration.
Quite possibly RH, however I always fish out any larger stuff first. We are seasonally prone to weather borne red dust that settles at the bottom & it is this that I've found is vacced up far more efficiently since the sand change. As said, only a guess that it's relative but long may it continue or at least until the dust has abated.
This is an interesting point:
RH, the logic is sound, they call it filter ripening. Due to the variations in sand the performance varies but generally 20-30 microns is the very best sand can achieve so relying on fines to aid the sand.

AFM glass filters to 4-5 microns and requires no ripening, in fact we don't want anything left to dirty the filter as dirt is a hide out of bacteria and pathogens and as the filtration media is the largest surface area in contact with the water and why in the past people have had sporadic issues with sudden changes in the water.

One reason the suction could improve is the new filter media is clean, I realised several years back how badly some domestic filters backwash, they simply do not clear the fine silt etc which builds up over time reducing the flow, this is only noticed when fresh media is fitted.

Although AFM does not need changing if the filter is not back washing well it may well silt up and require manual intervention.

Interestingly single speed pool pumps are often way too fast for good filtration and too slow for good backwash, in short they are a compromise.

My work on filters is to produce a filter that back washes better but other things frequently get in the way so progress is slow.
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teapot
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Post by teapot »

SW31 wrote:Just out of interest, what amount of sand do you need in the filter. The reason I ask is that we’ve had to do a lot of backwashing- partly due to guests literally slathering on sun cream. The filter now looks very clean Do you ‘lose’ some sand when you backwash and if so how much should you top it up with?
The level would be roughly half way up the filter.

Interestingly single speed pool pumps are often way too fast for good filtration and too slow for good backwash, in short they are a compromise. However sometimes they are too powerful and filter media/sand can be lost. This is partly due the the short squat shape of many filters. The German DIN standard requires complying filters to be taller than the squat models seen more frequently. That means there is more space to the filter bed to expand to release dirt etc before the filter media/sand is lost.
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