Frequiency Of Backwashes

[jaideeguy]

I've read many conflicting suggestions about the frequiency of backwashes on many 'swimming pool' forums.......some say as often as you want, some say when your pressure goes up 5psi, and another said least as possible because a particle build up can add to filtration of smaller particles.

I've tried frequient backwashes with no luck...meaning that i get fine particles returning to pool.

Now, I'm trying 'no backwash' for a while and seeing how that works.

I just recently switched media from sand only to a magnesium/sand combo and replaced 5%+ of my water with slightly muddy klong water, to save my ground water pump working for 10 hrs as well as bringing down my ph. klong water tested at 6 on my scale and my ground water is almost 8. Pump and filter have been running 10+ hrs and water is slowly clearing and no noticeable increase in pressure.

Just wondering what other's theories are on frequiency of backwashing??

[Chang_paarp]

You seem to have a couple of issues here.

1) Fine particles returning to he pool.

2) Backwash issues.

3) Water quality, source water especially.

Sand filters are not perfect by their nature, with a good quality sand they trap reasonably fine particles (sorry I have forgotten the numbers), changing from silicon sand to other media can improve the filtering of the water. If you have a pump that is too large for the filter it can push the finner particles straight through the filter media. Another issue is the spreader at the entrance of the filter, it is meant to make the water have an even coverage over the sand/media bed, if this is not correct the water can channel through the media and reduce the effectiveness of the filter. Some particles are too fine to be filtered by the sand filter.

Backwashing should be done as required, the indicator is the pressure guage. I am not familiar with psi , so I will use Kpa the unit I am used to looking at (some smarty will give you a conversion). On most domestic pools I have dealt with, the starting pressure of a clean pool is about 90Kpa, this rises to about 120kpa then backwashing is required. Providing the backwash is successful, the pressure returns to 90kpa. These number vary with some systems, small pipes, small filter, big pump, lots of sharp bends the initial presure is higher and the reverse is true. Remember that pump efficiency decreases with greater back pressure. (Most pumps have a spec sheet that shows this, otherwise vust look at the reduced return to the pools as the pressure get higher.)

Getting rid of fine particles, especially clay particles (less than 0.03mm) is best done with the aid of a clarifier. This is a chemical the makes the small particles stick together so they can be filtered or pumped out of the pool. The cheapest and most aggressive is alum, easily bought in Thailand, ask for สารส้ม it works best at a Ph of about 8.0 .

The best way to get rid of the fine stuff is,

1. fill the pool right up put the filter onto recirculate,
   
2. add the clarifier, stir up the water for a day (run pump),
   
3. turn the pump off and let everything settle for a 12 hours or more,
   
4. then vaccum the pool to waste, pumping the stuff straight out not through the filter.
   

This is the simplest way to get rid of the gunk.

When I was maintaining pools I would use a liquid clarifier as a regular thing for sand filters to keep the fine stuff under control. You notice it when the light is at the right angle.

One other thing, when you finish back washing, do a short (30-90 seconds) cycle with the filter on waste before you put the filter back to the filter position, this runs the water through the filter normally and the out the waste, it settles the filter media that has just been shaken up with the back wash and gets rid of any stray fine stuff before you start filtering again.

[Naam]

I've read many conflicting suggestions about the frequiency of backwashes on many 'swimming pool' forums.......some say as often as you want, some say when your pressure goes up 5psi, and another said least as possible because a particle build up can add to filtration of smaller particles.

there is no rule concerning frequency. pools are exposed to various degrees of dirt accumulation. easiest way to find out whether a backwash is required:

-switch multiport valve to backwash

-backwash for one, max two minutes

-watch whether water in "check glass" gets dirty

if water remains clear = backwash not required, respectively useless. it does not necessarily mean that your filter works as it should work.

[jaideeguy]

Hey Chang,

Thanks for your informative reply. I'll reply to your comments

' If you have a pump that is too large for the filter it can push the finner particles straight through the filter media'

I have a 2 hp pump and a 30" sand filter, is that oversized on the pump?

' Another issue is the spreader at the entrance of the filter'

seemed intact the last time i had the lid off, but will check again.

'Backwashing should be done as required, the indicator is the pressure guage'

mine is in psi and it consistently reads 18-20 psi unless i partially close an intake valve and it drops a little. I've always waited for the pressure to increase after not backwashing for a long time, but not. in fact i am now filtering the 'pea soupe' that i pumped from the klong. 15 hrs now and clearing somewhat, but pressure is still the same.

'The cheapest and most aggressive is alum'

That's what I used[3kilos]. pre klong water water and maybe will use it again now that 90% clear. and i used it according to your suggestion, but vacuuming to waste uses up lots of water.

One question...what about using a little alum in the filter, introduced thru the skimmer to catch the fines as they enter, then backwashing to waste after it clears 100%?? I had read that somewhere on a pool forum.

Thanks again for your input.

[jaideeguy]

And

"there is no rule concerning frequency. pools are exposed to various degrees of dirt accumulation. easiest way to find out whether a backwash is required:

-switch multiport valve to backwash

-backwash for one, max two minutes

-watch whether water in "check glass" gets dirty

if water remains clear = backwash not required, respectively useless."

Yeah Naam, that has mostly been my 'rule of thumb'....i can actually view my waste water going into the klong and run the backwash until the water runs clear, then rinse for a minute.

thanks

[Naam]

One question...what about using a little alum in the filter, introduced thru the skimmer to catch the fines as they enter, then backwashing to waste after it clears 100%?? I had read that somewhere on a pool forum.

nice try JD-Guy and no harm in doing that. however PAC won't stay in the filter and "catch the fines as they enter" as the chemical dissolves immediately, is pumped in the pool and will do there it's flocculation job. i am sure you came up with the idea to save on backwashing time, isn't it?

[jaideeguy]

Not so much to save backwashing time, but to stop this endless cycle of backwashing to waste, then refilling the pool with my calcium laden well water or the clay laden klong water, then flocculent, backwash etc.

I've now removed 97.8 % of fine particles and the rains are here, so I may backwash and let mother nature refill the pool. but the guy that installed the filter media advised against using rainwater because of algae blooms........any thoughts on rainwater causing algae??

[cloudhopper]

... but the guy that installed the filter media advised against using rainwater because of algae blooms........any thoughts on rainwater causing algae??

That seems a bit of a stretch to me. Although the rain water we collected on our boat during the NE season was frequently sooty (from PRC coal burning was my guess), the SW rains coming off the ocean seem fairly clean. Maybe a huge amount of rain water could temporarily dilute your Cl etc. levels enough to let the algae bloom?

I just bought some alum to try since I'm out of PAC but it was in fairly large crystals so should I try to pulverize them before throwing in the pool?

[Naam]

Not so much to save backwashing time, but to stop this endless cycle of backwashing to waste, then refilling the pool with my calcium laden well water or the clay laden klong water, then flocculent, backwash etc.

I've now removed 97.8 % of fine particles and the rains are here, so I may backwash and let mother nature refill the pool. but the guy that installed the filter media advised against using rainwater because of algae blooms........any thoughts on rainwater causing algae??

obviously it does. i realize that with my pond but have no idea why

[Naam]

... but the guy that installed the filter media advised against using rainwater because of algae blooms........any thoughts on rainwater causing algae??

That seems a bit of a stretch to me. Although the rain water we collected on our boat during the NE season was frequently sooty (from PRC coal burning was my guess), the SW rains coming off the ocean seem fairly clean. Maybe a huge amount of rain water could temporarily dilute your Cl etc. levels enough to let the algae bloom?

I just bought some alum to try since I'm out of PAC but it was in fairly large crystals so should I try to pulverize them before throwing in the pool?

i buy PAC as a very fine powder. try to dilute the crystals in a bucket. however, i don't see any harm applying the crystals in the pool directly. it just takes longer till they dissolve and start "working".

[jaideeguy]

I just went thru that.....the alum crystals and dilution and even used warm water to speed up dilution, worked a little, then just broadcast the remaining undisolved and it eventually dispersed. was recomended 3-4 kilos for my 80 cu mtr pool.

[cloudhopper]

I just went thru that.....the alum crystals and dilution and even used warm water to speed up dilution, worked a little, then just broadcast the remaining undisolved and it eventually dispersed. was recomended 3-4 kilos for my 80 cu mtr pool.

OK well I just smashed up the crystals as best I could. They didn't seem to dissolve very noticeably in the bucket so I broadcast the 2 kg I had after bringing the water up to pH 8. Will let it settle tonight then vacuum it all out tomorrow and let you know what happened...

[Gary A]

I really never paid much attention to the filter pressure gauge. A dirty filter cleans better than a clean filter. I always watched the outlet flow and the suction for the vacuum. When they were noticeably weaker I back washed the filter. I used a clear drinking water glass and caught some backwash water. When the water was clear, that was enough. If you can't sample the back wash water, the sight glass is better than nothing but catching water in a clear jar of glass is better.

[jaideeguy]

'OK well I just smashed up the crystals as best I could. They didn't seem to dissolve very noticeably in the bucket so I broadcast the 2 kg I had after bringing the water up to pH 8. Will let it settle tonight then vacuum it all out tomorrow and let you know what happened... '

CH, hopefully you ran your pump on recirculate for a few hours to spread the alum...and it took 2 days for mine to settle to bottom.

I suspect that you and I have the same problem [origin of suspended particles]....suspended calcium from hard water from well. Didn't we have a discussion on water softners a year ago. I got one and It seemed to work a little at first, but now, not. Did you get a water softner and is it doing any good??

and do you have calcium scale buildup on your tiles??

[cloudhopper]

'OK well I just smashed up the crystals as best I could. They didn't seem to dissolve very noticeably in the bucket so I broadcast the 2 kg I had after bringing the water up to pH 8. Will let it settle tonight then vacuum it all out tomorrow and let you know what happened... '

CH, hopefully you ran your pump on recirculate for a few hours to spread the alum...and it took 2 days for mine to settle to bottom.

I suspect that you and I have the same problem [origin of suspended particles]....suspended calcium from hard water from well. Didn't we have a discussion on water softners a year ago. I got one and It seemed to work a little at first, but now, not. Did you get a water softner and is it doing any good??

and do you have calcium scale buildup on your tiles??

It's recirculating now and I'll let it settle tonight (or longer). My water softener is working OK and we have no more scale buildups. Kind of a pain to maintain though and environmentally questionable. Anyway I had a check valve fail and half my pool water siphoned out the DAY after I had it perfect with PAC. So I replaced it with klong water and it was a real disaster - appears to have overloaded my sand filter with clay. So now I'm trying the alum since that's all I can get here in Pai.

[cloudhopper]

Update - the mia luang came back from town last evening with a huge bag of flaky alum strapped to the bike. I had already shut the pump off but since I had already brought the pH up to 8 with soda ash I broadcast a couple more kilos. This am the pool was clear enough to see the bottom and I vacuumed all the sediment out to waste. Still lots of stuff can be seen suspended so I'm going to repeat the same process except leaving the pH at 7.6 where it seems to be now. Also tried opening the vacuum valve on the pump manifold only half way and it seems to have significantly reduced the water wasted and still seemed to suck OK. The saga continues...

[Naam]

I had already shut the pump off but since I had already brought the pH up to 8 with soda ash I broadcast a couple more kilos.

why did you bring the pH up to 8?

[Naam]

A dirty filter cleans better than a clean filter.

in principle correct but NOT when PAC is used. vaccuuming sediments flocculated around PAC through the filter instead of the drain clogs the filter in no time.

[cloudhopper]

I had already shut the pump off but since I had already brought the pH up to 8 with soda ash I broadcast a couple more kilos.

why did you bring the pH up to 8?

Refer to post #2 above which I also confirmed on several other pool web pages. However there were 2 sites that said to keep the pH at 7. One said to do it along with superchlorinating. So there seems to be a difference of opinion out there, and I bet they all work OK! The alum itself appears to lower the pH somewhat as does the trichloroacetic acid, in contrast to PAC which I suspect is some organic charged polymer. The guy at the pool chemical shop in CM also recommended pH 8 for PAC as well BTW, at least in the context of precipitating out ferric/ous compounds that turn the water green..

[Naam]

I had already shut the pump off but since I had already brought the pH up to 8 with soda ash I broadcast a couple more kilos.

why did you bring the pH up to 8?

Refer to post #2 above which I also confirmed on several other pool web pages. However there were 2 sites that said to keep the pH at 7. One said to do it along with superchlorinating. So there seems to be a difference of opinion out there, and I bet they all work OK!

nothing unusual. ask 5 pool experts a question and you get 6 different answers that's why i stick to my own experience although i have to admit i learned a bunch of new things since i live in Thailand. most interesting was my pool builder ("we have built more than 300 pools") who told me soda ash as well as acid are meant to lower the pH besides that he has done in some respects an excellent job but went overboard with the number of inlet pipes and their dimensions. a pain in my àss is still that the volume of the overflow tank is to small and changing that would be painful²

[Naam]

'OK well I just smashed up the crystals as best I could.

only now i get it. you used alum not PAC

[jaideeguy]

Speaking of differences........I have the standard phenol red ph tester that reads my ph in the high 7's [almost 8] and recently got some test paper strips [the yellow kind] and it shows the same water at 7. Which one do I believe??

[cloudhopper]

Speaking of differences........I have the standard phenol red ph tester that reads my ph in the high 7's [almost 8] and recently got some test paper strips [the yellow kind] and it shows the same water at 7. Which one do I believe??

Believe that TIT. What are the gradation intervals on your paper strips?

[jaideeguy]

single digit for the paper strips, ranging 1-14.

the 'standard' phenol red tester runs from 6.8-8.2, as it's designed for swimming pool ranges.

keep us posted on your pool clearing.....

[cloudhopper]

single digit for the paper strips, ranging 1-14.

the 'standard' phenol red tester runs from 6.8-8.2, as it's designed for swimming pool ranges.

keep us posted on your pool clearing.....

Yeah definitely go with the dye instead of the strips for your pool.

Speaking of tests does anyone know how to test for "total alkalinity"?

So after the first alum session the water went from coffee brown to hazy blue grey. There was a white furry precipitate on the pool walls as well so I brushed the walls and floor which stirred up a fine cloud again. I broadcast another few kg. of alum flakes and this time instead of running the pump I let it settle for a full 24 hrs. This am the water looked pretty clear and the pool bottom had a fine precipitate so I once again vacuumed it all to waste. The precipitate was very fine and it was difficult to vacuum even slowly without stirring it up. Then I added Pooltrine clarifier and am again running the filter which hopefully will clear the suspended fine particles I can still see. Looking pretty nice now though. Note to self - never use klong water again for make up, at least in large quantities in the rainy season!

[jaideeguy]

Glad to hear that you beat the 'monster' in your pool CH. Mine is almost dead, but a little remains.....maybe another alum dose for him.

"total alkalinity"?....Oui at world chemicals sold me a bottle of purple test drops that you drop a couple into a sample and if it turns red...it's too much, or the other way around, anyway you can confirm the test by using a sample of reverse osmosis bottled water. I think cost was around 90baht.

With you living in Pai, I'm sure you could order supplies from him to be sent by bus or transport service.

BTW, what was your source of make up water this time??

[cloudhopper]

Glad to hear that you beat the 'monster' in your pool CH. Mine is almost dead, but a little remains.....maybe another alum dose for him.

"total alkalinity"?....Oui at world chemicals sold me a bottle of purple test drops that you drop a couple into a sample and if it turns red...it's too much, or the other way around, anyway you can confirm the test by using a sample of reverse osmosis bottled water. I think cost was around 90baht.

With you living in Pai, I'm sure you could order supplies from him to be sent by bus or transport service.

BTW, what was your source of make up water this time??

Fortunately I have a productive well but every time I backwash the water softener I flush 10kg of salt into my spring fed pond - can't be good. In fact I'm starting to think between the electricity the pump uses and all the chemicals like the alum that's going "somewhere" the whole pool thing is not very environment friendly. Maybe it will become a big algae oil bioreactor someday! I just re-plumbed my filter output into a nice looking waterfall and decommissioned the underwater inlets so there is now no way to lose half my pool water again due to a component failure anyway....

[Chaichara]

One other thing, when you finish back washing, do a short (30-90 seconds) cycle with the filter on waste before you put the filter back to the filter position, this runs the water through the filter normally and the out the waste, it settles the filter media that has just been shaken up with the back wash and gets rid of any stray fine stuff before you start filtering again.

This is false. After backwashing the valve is put into the RINSE position to reverse thr flow through the filter medium to the waste pipe. The WASTE position of the MPV bypasses the filter material completely - you will just be throwing good water away. SiamConsulting used to have a downloadable PFD on their site which you could print and laminate for your pumphouse. It doesn't seem to be there now but you could ask them. It was free.

[Naam]

One other thing, when you finish back washing, do a short (30-90 seconds) cycle with the filter on waste before you put the filter back to the filter position, this runs the water through the filter normally and the out the waste, it settles the filter media that has just been shaken up with the back wash and gets rid of any stray fine stuff before you start filtering again.

This is false. After backwashing the valve is put into the RINSE position to reverse thr flow through the filter medium to the waste pipe. The WASTE position of the MPV bypasses the filter material completely - you will just be throwing good water away. SiamConsulting used to have a downloadable PFD on their site which you could print and laminate for your pumphouse. It doesn't seem to be there now but you could ask them. It was free.

correct!