Bag Filters - Case Study

[AllanB]

About a year ago I raised the topic of using bag filters, which was/is a growing trend among pool manufacturers, but which attracted a lot of criticism among the pool professionals (their words not mine) on this forum. So, two of us who have pools with bag filters, my friend Barry's is 2 1/2 years on, mine is just 18 months, is a reasonable case study. Oh, and both pools have roofs too, anyway I would like to share our findings with you.

Barry's fiberglass pool has a salt water chlorinator, he runs his pump for 4 hours daily, instead of the 6 hours recommended, the 5 micron bag is cleaned once a week and all is still well. The pool is vacuumed every two weeks, so he spends about 1 hour a week on very simple cleaning maintenance of the whole pool area. Without a big bulky sand filter and valves, there is no plant-room and the pool water (still original) is pristine and inviting.

Mine has been a similar story in terms of results, but achieved in a less conventional way with "ultra economy" in mind (yes, I am tight-arse) and the key, I believe, has been the 1 micron bag filter.

Throughout the life of the pool, on average I run my main 1 hp pump for about 1 hour a day using a 50 micron main filter, but my weekly cleaning routine involves 2 phases, both employing a superfine 1 micron bag filter. I first clean the pool, which takes about 30 minutes, but then leave the 250 watt pump running for a few hours to remove any fine suspended solids, bacteria, etc.,indeed anything above 1 micron in size is extracted. Effectively removing material instead of destroying it with chlorine, plus my dubious quality top-up water is first passed through the bag before it enters the pool.

I use chlorine pucks dropped into the trough and shock every 2-3 weeks or so, dropped directly into the pool and have twice needed to use ph+..

I would start by saying that my 8 x 4 pool has a very efficient infinity edge draining system and a simple steel roof covers the entire pool area, which, I believe are huge plus points in this climate.

Running costs:- Looking back through my last 12 months of records I note the following costs:-

3off 5kg boxes of pucks

2off 5kg boxes of shock

1off 5kg box of ph+ (50% still left)

About 350kWh hours of electricity.

2 replacement bag filters.

Things that people warned me would happen are as follows:-

1. I was told by a "pool expert" that a blocked filter bag would be sucked into the pump and I pointed out that to be theoretically impossible. What happened in practice was that when the filter became blocked it reduced the flow of the pump. So the same as any pool filter.

2. I was told that, due to the roof, the water temperature would be too low for Thai people, as well as some Farangs and that has proved to be the case, though now the weather is very hot, it is pretty much perfect. However, with the flat roof, a simple solar water heater would solve that problem, at a cost of a hundred meters of plastic hose.

3. I was told that the pump should be run for a much longer daily periods, otherwise algae would become a problem, but this hasn't been the case, for a few reasons. a) With virtually no pressure drop across the bag filter the pump achieves full flow. The infinity edge is a very efficient method of exiting dirt from the pool. c) The cleaning pump with a 1 micron filter removes algae spores and other microscopic undesirables, dead or alive..

Conclusion:- Would I do anything differently?

1. Yes, I would make the pool 10 metres long even if it meant being slightly narrower.

2. I would probably go a little deeper too, 1.3 - 1.4 metres (water depth) would be ideal.

3. I would make the trough bigger than the 1 m3, to avoid constant topping up. 1mm pool loss due to evaporation = 40mm in the trough level and surges exacerbate the problem.

4. Oh and the two small water features don't work very well, so they will be changed.

5. I would import many more bag filters, as I am now selling them.

Would I recommend any of the features of my pool:-

1. Bag filters knock everything else into a cocked at, they are cheap to buy, easy to clean and can even be sterilised during washing. They place almost zero load on the pump, lowering running costs and extend the life of the pump.

2. The roof makes a huge difference to the water quality and enjoyment of the pool, with round the clock usage possible even in the blistering hot mid day sun.

3. The infinity edge, the most efficient cleaning method, no doubt.

My next project is to alter the water entry system to the pool, using two big urns, providing falling, aerated water feeds and I will install a 1 micron filter bag in each urn, for obvious reasons.

I hope this gives some of you new pool builders some fresh ideas and if you have any of your own please post them and share..

[tollgate]

Allan - why do you shock your pool every 2 to 3 weeks? I have had my pool for 15 months now and only had to shock once after a "fecal incident".

Do you have any pictures of your pool and bag filter system?

[AllanB]

Allan - why do you shock your pool every 2 to 3 weeks? I have had my pool for 15 months now and only had to shock once after a "fecal incident".

Do you have any pictures of your pool and bag filter system?

That is a very interesting point Tollgate, advice from others, I guess, including the chlorine suppliers, but will stop now to see what happens.

My next plan is to stop using pucks and only use shock, every 2 - 3 days, as recommended by the chemical suppliers, that means only 15kg of chlorine for a whole year, 2500baht for everything.

I may even cut down on that, since I clean the pool through 1 micron filter, which does the same job as the chlorine....and I have a roof too.

There is so much crap advice out there, a lot of it coming from so called experts, here is a typical example

Note my comments underneath.

I think the main problem is they want to sell you stuff and that leads to BS, soon everyone believes the BS because they think they are listening to professionals and trust them. You are much better off speaking to the end user, who has no vested interest.

A good example of this is the TV motorcycle forum, who are just a bunch of guys trying to help each other, the result is that you get genuine advice and solve your particular problem.

[Naam]

Allan - why do you shock your pool every 2 to 3 weeks? I have had my pool for 15 months now and only had to shock once after a "fecal incident".

Do you have any pictures of your pool and bag filter system?

That is a very interesting point Tollgate, advice from others, I guess, including the chlorine suppliers, but will stop now to see what happens.

My next plan is to stop using pucks and only use shock, every 2 - 3 days, as recommended by the chemical suppliers, that means only 15kg of chlorine for a whole year, 2500baht for everything.

I may even cut down on that, since I clean the pool through 1 micron filter, which does the same job as the chlorine....and I have a roof too.

There is so much crap advice out there, a lot of it coming from so called experts, Note my comments underneath.

I think the main problem is they want to sell you stuff and that leads to BS, soon everyone believes the BS because they think they are listening to professionals and trust them. You are much better off speaking to the end user, who has no vested interest.

A good example of this is the TV motorcycle forum, who are just a bunch of guys trying to help each other, the result is that you get genuine advice and solve your particular problem.

i agree with "there is so much crap advice out there..." but object as fas as your statement "I may even cut down on that, since I clean the pool through 1 micron filter, which does the same job as the chlorine... and I have a roof

too" is concerned.

neither the 1µ filter bag nor the roof over your pool prevents the development of certain bacteria, many of which are sized between 0.2 and 0.5µ. in my [not so] humble view additional sanitising/shocking is therefore mandatory to achieve top quality pool water.

i also object to "tollgate's" claim "I have had my pool for 15 months now and only had to shock once after a "fecal incident" except if he has carried out a rather expensive bacterial check by a qualified lab. reason: "fecal incident" means most probably E.Coli bacteria.

i have a completely enclosed pool (pool area airconditioned) which i keep between 0.2 and 0.5ppm CL and use during daily two hours of filter time a UV sanitiser matching 150% of my pool pumps capacity of 400l/min. inspite of that i wouldn't feel comfortable without shocking the pool every 3 months with 5-7ppm CL.

[tollgate]

Naam - I don't see why I should need to shock. I check my free chlorine every evening. It's normally between 3 to 5 ppm. Adding one litre 10% bleach brings it up to 5 to 7 ppm. This is with CYA of 50 ppm. I would only shock the pool if my free chlorine suddenly fell close to zero or the combined chlorine was above 1 ppm. To shock I would have to raise the free chlorine to around 16 ppm. I guess you have zero CYA in your pool as you only have 0.2 - 0.5 FC?

[AllanB]

Allan - why do you shock your pool every 2 to 3 weeks? I have had my pool for 15 months now and only had to shock once after a "fecal incident".

Do you have any pictures of your pool and bag filter system?

That is a very interesting point Tollgate, advice from others, I guess, including the chlorine suppliers, but will stop now to see what happens.

My next plan is to stop using pucks and only use shock, every 2 - 3 days, as recommended by the chemical suppliers, that means only 15kg of chlorine for a whole year, 2500baht for everything.

I may even cut down on that, since I clean the pool through 1 micron filter, which does the same job as the chlorine....and I have a roof too.

There is so much crap advice out there, a lot of it coming from so called experts, Note my comments underneath.

I think the main problem is they want to sell you stuff and that leads to BS, soon everyone believes the BS because they think they are listening to professionals and trust them. You are much better off speaking to the end user, who has no vested interest.

A good example of this is the TV motorcycle forum, who are just a bunch of guys trying to help each other, the result is that you get genuine advice and solve your particular problem.

i agree with "there is so much crap advice out there..." but object as fas as your statement "I may even cut down on that, since I clean the pool through 1 micron filter, which does the same job as the chlorine... and I have a roof

too" is concerned.

neither the 1µ filter bag nor the roof over your pool prevents the development of certain bacteria, many of which are sized between 0.2 and 0.5µ. in my [not so] humble view additional sanitising/shocking is therefore mandatory to achieve top quality pool water.

i also object to "tollgate's" claim "I have had my pool for 15 months now and only had to shock once after a "fecal incident" except if he has carried out a rather expensive bacterial check by a qualified lab. reason: "fecal incident" means most probably E.Coli bacteria.

i have a completely enclosed pool (pool area airconditioned) which i keep between 0.2 and 0.5ppm CL and use during daily two hours of filter time a UV sanitiser matching 150% of my pool pumps capacity of 400l/min. inspite of that i wouldn't feel comfortable without shocking the pool every 3 months with 5-7ppm CL.

I didn't say I would eliminate the chlorine just cut down, the roof on it's own helps a lot with the chlorine usage and by the sound of it, you aren't using much at all at a level of 0.2 and 0.5. I am looking at dropping down to 1ppm.

You are correct that E.Coli is unlikely to be filtered out with my set up, so the "jobby" incident would be a super-chlorination case to my mind.

All this is moving in the right direction as far as I am concerned, less chemicals means less chemicals to counter the chemicals, less risk and less money spent. The big bad 2 I stay clear of are the 2 metal sulfates, copper and aluminium, you must be mad putting those in the water, water companies spend millions trying to take them out.

An indoor pool, eh, very good, do you heat the water during the winter?

[Naam]

Naam - I don't see why I should need to shock. I check my free chlorine every evening. It's normally between 3 to 5 ppm. Adding one litre 10% bleach brings it up to 5 to 7 ppm. This is with CYA of 50 ppm. I would only shock the pool if my free chlorine suddenly fell close to zero or the combined chlorine was above 1 ppm. To shock I would have to raise the free chlorine to around 16 ppm. I guess you have zero CYA in your pool as you only have 0.2 - 0.5 FC?

your average free CL is already very high Tollgate and 7ppm is in my book = shock. but if you google for "expert" advice you get a dozen different opinions.

your assumption "zero CYA" in my pool is correct because of no sun except the UV radiation i apply.

[Naam]

Allan - why do you shock your pool every 2 to 3 weeks? I have had my pool for 15 months now and only had to shock once after a "fecal incident".

Do you have any pictures of your pool and bag filter system?

That is a very interesting point Tollgate, advice from others, I guess, including the chlorine suppliers, but will stop now to see what happens.

My next plan is to stop using pucks and only use shock, every 2 - 3 days, as recommended by the chemical suppliers, that means only 15kg of chlorine for a whole year, 2500baht for everything.

I may even cut down on that, since I clean the pool through 1 micron filter, which does the same job as the chlorine....and I have a roof too.

There is so much crap advice out there, a lot of it coming from so called experts, Note my comments underneath.

I think the main problem is they want to sell you stuff and that leads to BS, soon everyone believes the BS because they think they are listening to professionals and trust them. You are much better off speaking to the end user, who has no vested interest.

A good example of this is the TV motorcycle forum, who are just a bunch of guys trying to help each other, the result is that you get genuine advice and solve your particular problem.

i agree with "there is so much crap advice out there..." but object as fas as your statement "I may even cut down on that, since I clean the pool through 1 micron filter, which does the same job as the chlorine... and I have a roof

too" is concerned.

neither the 1µ filter bag nor the roof over your pool prevents the development of certain bacteria, many of which are sized between 0.2 and 0.5µ. in my [not so] humble view additional sanitising/shocking is therefore mandatory to achieve top quality pool water.

i also object to "tollgate's" claim "I have had my pool for 15 months now and only had to shock once after a "fecal incident" except if he has carried out a rather expensive bacterial check by a qualified lab. reason: "fecal incident" means most probably E.Coli bacteria.

i have a completely enclosed pool (pool area airconditioned) which i keep between 0.2 and 0.5ppm CL and use during daily two hours of filter time a UV sanitiser matching 150% of my pool pumps capacity of 400l/min. inspite of that i wouldn't feel comfortable without shocking the pool every 3 months with 5-7ppm CL.

I didn't say I would eliminate the chlorine just cut down, the roof on it's own helps a lot with the chlorine usage and by the sound of it, you aren't using much at all at a level of 0.2 and 0.5. I am looking at dropping down to 1ppm.

You are correct that E.Coli is unlikely to be filtered out with my set up, so the "jobby" incident would be a super-chlorination case to my mind.

All this is moving in the right direction as far as I am concerned, less chemicals means less chemicals to counter the chemicals, less risk and less money spent. The big bad 2 I stay clear of are the 2 metal sulfates, copper and aluminium, you must be mad putting those in the water, water companies spend millions trying to take them out.

An indoor pool, eh, very good, do you heat the water during the winter?

heating season for our pool is october till end of march. till last year heating was done by a 36k btu/h airconditioner cooling the pool area and at the same time heating the water. but then i convinced a local pool builder to import solar panels and had ~20m² installed. the heating capacity of the aircon was just not enough to keep the pool water at a comfortable 28-29ºC november till february.

[AllanB]

I am thinking of chucking up a few metres of plastic hose onto my flat roof (there's posh) and putting my submersible pump water through it.

Somebody told me about high efficiency submersible pumps which they use for fish ponds, so that could be run all day. In any case the system would be dual purpose, with the flow being put through a 1 micron bag filter.

I am not looking for 28-29, a few degrees above normal will be fine, you soon get warm with a quick burst of muscle power.

[Naam]

I am thinking of chucking up a few metres of plastic hose onto my flat roof (there's posh) and putting my submersible pump water through it.

Somebody told me about high efficiency submersible pumps which they use for fish ponds, so that could be run all day. In any case the system would be dual purpose, with the flow being put through a 1 micron bag filter.

I am not looking for 28-29, a few degrees above normal will be fine, you soon get warm with a quick burst of muscle power.

"a few meters" is not enough but i like the idea of combining filtering with heating. that's what i am doing now because filter time is nearly identical with required heating time. that would have been impossible with my former pool because we had winter nights with temperatures down to freezing or below and still maintained a minimum of 27ºC pool water (too cold for the Mrs).

[AllanB]

Naam - I don't see why I should need to shock. I check my free chlorine every evening. It's normally between 3 to 5 ppm. Adding one litre 10% bleach brings it up to 5 to 7 ppm. This is with CYA of 50 ppm. I would only shock the pool if my free chlorine suddenly fell close to zero or the combined chlorine was above 1 ppm. To shock I would have to raise the free chlorine to around 16 ppm. I guess you have zero CYA in your pool as you only have 0.2 - 0.5 FC?

your average free CL is already very high Tollgate and 7ppm is in my book = shock. but if you google for "expert" advice you get a dozen different opinions.

your assumption "zero CYA" in my pool is correct because of no sun except the UV radiation i apply.

Why do you think that is Naam, is it that 11 of them are fools?

I think the problem is the lack of science here, all these "experts" are nothing more than salesmen reading from brochures and then guessing. And even if there were a chemical engineer among them, with a different chemicals throw in for just about everything, analysing the mess would be impossible. In any other industry where public safety is at risk there are regulations, not so with the pool industry.

I am no chemical engineer myself and don't try to be. This is why I am so interested in bag filtration, there are many things a bag filter can do that other filters can't, including replacing a number of chemicals.

One of the things I am looking at now is putting a bag filter on the discharge to the pool, an urn or two with a 1 micron bag inside it, feeding the pool with "polished water". No load on the pump and low cost too, unless you have expensive tastes in pottery.