Backfwash with glass filter media - WORRY

[EricHoudini]

I've got equipment of ASTRAL, with glass media in the filter instead of sand, which is said to be much better, perhaps, surely more expensive.

Where as I had to backwash my sand filter in Switzerland every 1 or 2 weeks due to pressure/resistance increase, caused by build-up of dirt on/in the filter, the pressure here never increases into the red zone requiring backwash. I backwash sometimes after vacuuming, but not always. I haven't opened the filter to check whether there is any glass left inside, though the pool water is clear, hence I believe the filter serves the purpose of filtering out course and fine particles.

Can you comment on your experience with glass filter media, on backwash and other points, please.

Thanks.

[SwimmingPoolsThailand]

The answer to this is basically: 'If it ain't broke, don't fix it'



- if your filtration plant is doing what it's supposed to do then it's doing what it's supposed to do, although ask such questions of a pool 'professional' and chances are he will immediatey see an opening to convince you of buying something. Filter media does not get lost or used up. Avoid backwashing too frequetly - again you'll only be throwing water with its valuable chemicals to waste and doing your pool shop a favour by buying more.

Filter sand and crushed recycled bottle glass are basicaly the same thing: silicon dioxide. Google 'glass filter media' and 'silicon dioxide' and you'll get several pages of results all from various brands claiming to be manufacturers of a revolutionary new product for swimming pool filters. In fact all they do is recover the glass from the bottle banks, wash it, crush it, grade it, wash it again, and pack it attractively for resale.

Crushed glass does however have a somewhat better performance than sand and while it is more expensive, the better choice would actually be zeolite, a volcanic product that will filter better still (better even than D.E.), lasts longer, and has some properties that the other media do not have. 



Download an independent scientific study about glass filter media from
 www.cwc.org/glass/gl981rpt.pdf 
and visit our website at FILTER MEDIA to learn more, see the prices, and download the producers' brochures. For the pools we construct, we fill the fiters with Zelbrite (zeolte) by default because it does not impact on the price of a complete pool project. We sell filter sand in 50 Kg bags, glass media in 25 Kg bags, and Zelbrite in 15 Kg bags. We distribute about 40 ton of Zelbrite a year in Thailand although some importers may sell more. We sell less than a ton of crushed glass.

[SantiSuk]

On the same, if it aint broke, principal my pool project was delivered with normal pool sand. Have been perfectly content with its performance so never really bothered to think about the alternatives that some people rave about. I also find in Thailand that my pressure gauge never gets anywhere near red, but after about 3 months I notice fine sandy dirt coming up through the returns to rest on the bottom, so I take that that as my signal to backwash. I replaced the sand (via Poolstore) when that 3 month cycle noticeably dropped to 2 months - that was after 2.5 years so maybe standard sand doesn't last quite as long as the 3 years people usually quote.

[SantiSuk]

On the same, if it aint broke, principal my pool project was delivered with normal pool sand. Have been perfectly content with its performance so never really bothered to think about the alternatives that some people rave about. I also find in Thailand that my pressure gauge never gets anywhere near red, but after about 3 months I notice fine sandy dirt coming up through the returns to rest on the bottom, so I take that that as my signal to backwash. I replaced the sand (via Poolstore) when that 3 month cycle noticeably dropped to 2 months - that was after 2.5 years so maybe standard sand doesn't last quite as long as the 3 years people usually quote.

Should have said "never gets into yellow"

[sappersrest]

Do not panic if it is not broke leave it alone, but a bit of background info for you.

Glass is a first class filter medium , and works extremely well, have used many hundreds of tonnes in the past few years.

Also sand and Zelbrite are good though I have not had any personal experience off the later.

One of the main problems that arise with pool filters both commercial and domestic, Is getting the filtration rate correct often many installers will fit too large a pump and the results are that dirt a chemical salts are pushed to the middle and bottom of the filter , then when the filter is backwashed the media is not fluidised correctly and so not cleansed resulting in more frequent backwashes.

The optimum pool filtration is what is call medium rate and is around 20m/3 per hour of water per m/2 of filter and the optimum backwash rate is 28m3 / hour per sq meter of filter.

Many filter manufacturers give a lot higher rate on their data sheets but in most cases these are the maximum figures.

Yes once you have done the calculations you will be surprised e.g. an average 25 m x12 m pool with a 2.5 hour turnover will require around 7 sq m of filter area???

[IMHO]

In reference to gauges getting "into the red" -I always thought the rule of thumb was to backwash/clean when the filter pressure gets to +5 PSI over nominal. Which on my filters (1 sand, 1 cartridge) is nowhere near the red or yellow zone. Am I doing it wrong?

Either way, it works I suppose. My sand filter needs backwashing every week or so, my cartridge filter needs rinsing every 2-4 weeks... It's very dusty around here though.

Side note: Once my sand filter becomes unserviceable, i'll be putting it in the bin and replacing it with a cartridge. They need cleaning less often, waste far less water to clean, washing doesn't waste pool chems, plus the waste water from washing isn't laced with pool chems - so you can dump it wherever it's useful - like the garden, not just the down the drain. And on top of all that, the water they filter looks so much clearer under pool lights. All win, no lose, IMHO.

[sappersrest]

In reference to gauges getting "into the red" -I always thought the rule of thumb was to backwash/clean when the filter pressure gets to +5 PSI over nominal. Which on my filters (1 sand, 1 cartridge) is nowhere near the red or yellow zone. Am I doing it wrong?

Either way, it works I suppose. My sand filter needs backwashing every week or so, my cartridge filter needs rinsing every 2-4 weeks... It's very dusty around here though.

Side note: Once my sand filter becomes unserviceable, i'll be putting it in the bin and replacing it with a cartridge. They need cleaning less often, waste far less water to clean, washing doesn't waste pool chems, plus the waste water from washing isn't laced with pool chems - so you can dump it wherever it's useful - like the garden, not just the down the drain. And on top of all that, the water they filter looks so much clearer under pool lights. All win, no lose, IMHO.

Yes you are correct with the 5 psi above normal .Normal is the reading you obtain after the filter has settled in after a filter refill and a couple of rinses.

Remember cartridge filters are extremely efficient, make sure you get one of sufficient surface area,otherwise you will be washing it every few days a good supplier should be able to work this out for you it all depends on required turnover time required and pump size.