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If they are backwashing daily, replace the top 3" of sand and try to stir the rest. Check for filter problems.
Rob Lane
Thank you so much for your comments. I really enjoy getting the technical feedback and the details in your explanations. Very much appreciated. I have put forth a proposal to my client to use the zeolites but it has to pass the budget meeting first.
I get what you guys are saying about the channeling of the media but shouldn't the sand/zeolite get disrupted and tossed around during the backwash cycle so that you eliminate any "dead" spots? The filers are in the 26"-36" size range. I understood that the channeling was more likely in a larger or horizontal sand filter. The operators are quite good at backwashing the filters for the recommended 3-5 min. At peak usage they are sometimes backwashing daily.
However, from observations of thousands of pool reports on pool forums from residential pools, many with sand filters, I don't think the aforementioned issues are as common in such pools. One rarely sees the kind of high chlorine demand, even overnight (when such demand should be measured, with the pump running vs. not running), that would be seen if such problems were occurring -- at least when pools are consistently and properly maintained with chlorine. Also, when pool owners have replaced their sand, only a very, very small number saw channeling in the filter (we're talking perhaps two incidents out of a hundred or so sand replacements). I believe I've seen numbers quoted by others for channeling in traditional sand filters in commercial/public pools more like 30-40% or more. So I know this isn't very scientific, but my gut feel is that this bacterial growth problem in sand filters isn't as big a deal in residential pools. I'd be interested in hearing reports from others on this forum about the percentage of sand filter changes that appeared to have channeling or other evidence of biofilm formation in residential pools.
Nevertheless, I'll keep a lookout from this point forward on this issue and start polling pool users to try and identify such issues, as well as get more users to do overnight pump on/off tests where any chlorine demand from the filter contents should be able to be detected readily (using FAS-DPD chlorine tests measuring within 0.2 ppm FC and CC).
As for cartridge filters, I think it even less likely for there to be uneven water distribution or channeling to occur in such filters. Only if the chlorine level was too low or the filter not run frequently enough would I expect the potential for significant biofilm growth on such filters. Again, this is not only based on the lack of reported residential pool owner problems of this type, but the fact that the pool owners using BBB (basically, unstabilized chlorine with CYA already in the water at appropriate FC/CYA ratios) don't seem to have unusual chlorine demand or other issues even though they do not shock their pool at all or very infrequently. In my own cartridge filter that I've cleaned every year, after simple spray rinsing to get the bulk cedar needles and suntan lotion accumulation off of the filters, they do not appear to have any slimy biofilm remaining that I could see or feel (the filters are then soaked in TSP or equivalent) and there is virtually no change in either pressure or chlorine demand, in my case probably due to having an intentionally oversized cartridge filter. Most pool users with cartridge filters, however, have smaller (i.e. closer to minimum required sized) filters where a pressure rise is more common.
As for zeolite, I can't really comment on whether it is any better or worse than regular sand with regard to bacterial biofilm formation. Based on the above, I think the issue would be more relevant for commercial/public pools, but I really don't know if there are technical reasons why zeolite would inhibit bacterial growth or would resist channeling. Perhaps the tiny pore spaces prevent channeling (at least until such spaces get clogged until the next backwash), but that is speculation on my part. Zeolite presumably has better filtration capability due to these pores, though obviously one would need to backwash frequently enough to keep such pores open and I suspect that this clogging may occur well before a significant pressure rise is seen. Once the pores get clogged, zeolite operates much more like traditional sand as water moves around the zeolite "sand-like" particles, but there is a lot of pore volume so it may take a lot of fine particulate matter to clog them.
The comments about glass filtration media from Dryden Aqua (AFM) are in fact correct. Glass filtration media is definitely the way to go in the future.My company in Australia ,Poolrite Equipment is a full line manufacturer and supplier of filtration and sanitation equipment.
Four years ago we were made aware of the liability attached to sand in sand filters (the same would also i believe apply to zeolites).
Pentair were sued in the United States for the death and subsequent major illness of 30 odd people on a Carnival Cruise Line in the Carribean (legionairres).
Pentair did not make the sand only the filter but in a judgment 5 or 6 years ago were ordered to pay ,WAIT FOR IT............. $195 million for the deaths and destruction to carnivals business.On appeal it was overturned to $40 million,but that,s still a fair piece of change for the supply of a $500 filter housing.
On hearing this our company who makes tens of thousands of sand filters each year investigated alternatives and came up with recycled glass (it feels like sand).
Sand and Zeolites are porous substances ,the surface area of the media particles often exceed the surface area of the hard floors and walls,and pipes of a pool.
Bacteria creep into crevices and pores excreting alginates to protect themselves from chlorine. A gram of filter sand can can register a bacterial plate count of over 3,000,000. In glass because it is amorphous the count is less than 1 (not one million but one.)
In a lot of residential pools where the filtration is intermittent bacteria are not necessarily breeding in the pool but in the filter,especially in sand zeolites and cartridges.
The German Hygiene Institute of the Ruhr (HY) has 10 vans on the road collecting each on average 35 samples a day rushed back to their automated laboratory,where they measure
1.Trihalomethanes
2.Chloramines
and
3.Grow cultures looking for Legionella
This is a pay by user service for over 2000 German Public Pools which are using sand filters with active carbon beds.
We actually took a stand and even though the glass was 2.5 times the retail price of sand we refused to sell sand filters as such purely from a common sense and liability standpoint.
There were some sweaty palms for a while ,but the contractors saw the sense of it as armed with knowledge that there was a problem and a fix for it they embraced it.
Two of our competitors have now followed suit.
Every single system that goes out of our door is accompanied by glass media that we produce ourselves check out www.diamondkleen.com .
We now export it to Europe and South East Asia as well.
It traps much deeper in the bed and does not purely work on mechanical entrapment,but a combination of a surface charge and mechanical .
Time between backwashes is extended and chlorine consumption is down by a minimum 0f 30% (doesn,t have to be consumed by bacteria in the sand bed).
3.G
So zeolite has many fine properties of filtration, but the absorption of ammonia is only really useful in a pool that isn't well maintained with chlorine (which does happen sometimes -- unfortunately, pools can get to near zero FC under higher bather loads if the FC is initially too low and/or the control automation equipment does not respond quickly enough). If zeolite avoids forming channels the way that sand sometimes does, and if it inhibits bacterial growth in dead spots in the filter, then it can prevent chloramine formation in the filter itself from bacteria that can sometimes grow in sand filters. That is also the basis for Active Filter Media (AFM) from Dryden-Aqua (though that is a form of fine glass beads, not zeolite).
We too have used it for years and sell it out of the store as a replacement for sand. About the only downside is that you absolutely MUST backwash the filter thoroughly before putting it into filter mode. If you don't it will introduce a massive brown cloud. One of our service techs discovered this after not reading the instructions. Lessons are always best remembered when learned the hard way.
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