to backwash or not

[Frank]

I am a pool novice, Iam considering a 10 x 5  x1.5 metre pool , flat bottomed and have been told that if Iam not connected to the mains drains I cannot have a sand filter which requires regualr backwashing and should therefore opt for a cartridge type filter which does not require backwashing. The pool will be used by gite guests and I believe must therfore comply with DASS norms also. My maximum guest levels when fully open will be 18 persons plus my wife and I .

my questions are

chlorine or salt sanitization ( preference for the easiest to control and maintain)

sand or cartridge type filtration

how much water does backwash consume how often and can it be run to drain or soak away ( I have a 60 x 30 metre garden area)

I don't have mains drainage but have drain off from the roofs which exit the property into the main road outside probably road drains . can I utilise these ???

How much should I be looking to pay for a tractor digger to excavate the hole for me

Thanks in advance for your help

 

 

 

 

[Piprob]

Its pretty much a matter of choice. I chose chlorine because I decided it would be easier to close down and re-open either side of winter. We have a sand filter. You can see through the perspex filter housing when a back wash is necessary. I run back-wash for anything between 20 and 40 seconds depending on how long it takes the water to run clear. I need to back-wash at least once a week due to site conditions. After a 40 second burst, the water level in my 8x4 pools has dropped by around 3 cm - a lot!

If you have a pool liner and you use chlorine, you must take great care to control the water temperature; too hot for too long (above 28c) and you'll destroy the liner - especially if you leave it covered for several days. One benefit of salt is that it is more benign. But the close-down and open-up operation can (but will not necessarily always) take longer.

You may not be permitted to tip your chlorinated water into a surface water drain. You need to check locally. As for the cost of digging a hole - that depends entirely on how long it takes. Soil differs from place to place. You would be well advised to obtain a quote. A guess would be two men for a maximum of two days, assuming a mini-digger, and assuming you intend to leave the arisings on site.

[Baz]

Whilst backwashing is requirement of a chlorinated pool, it is worth pointing out that if the French water restrictions are reimposed as in 2005, then replacing the emptied water could cause a major problem.

I have a pool in Essex and whilst at present am not effected by Thames Water Board water restriction from next month. However, I am aware that if Anglian Water impose drought restrictions then use of  my pool may be very restricted with perhaps closure of the pool to be considered. Let's hope it rains for 2 months!!!

Baz

[Poolguy]

Jetlag

Thanks for

the question.

You have

asked a number of interesting questions, many of which will be a perpetual

problem for pool owners here in France.

As for the

First one.

You said

that somebody told you that you couldn’t own a sand filter because you are not

connected to the mains drain? Extraordinary!!! Who was it that told you that..

was it the Marie? Normally they will not get involved in those types of

decisions. They may insist on a separate fosse for the backwash but I have not

heard of them getting involved in filtration specification. You should know

that using a cartouche is not exempt from cleaning. You will be obliged to

remove and clean a cartouche once a week using the hose. Its much the same as

sand filtration as regards the consumption of water.

I suggest

that you consider a sand type filter but fill it with a product called ‘Aqua

Crystal’, which is one of the Zeolites. This will in effect reduce the need to

backwash to once every 2-3 weeks. It also gives you far better filtration than

sand, cartouche or even diatomaceous earth. So from a hygiene point of view,

you can not only economize on your use of water but you will more than comply

with the DDASS norms on filtration.

For the

problem of water, thankfully we are now off water restrictions (for the time

being) and the rivers once again look full and flourishing. However, it would

be smart to allow for the possibility of reintroduction of these restrictions.

The best provision would be to install rain water storage, which is nearly mandatory

in other parts of the world but a novelty here. If you store even 1 cubic

meter, then it’s better than nothing. However, for a full season top up on a 10

x 5, I suggest that a minimum of 10 cubic meters would be suitable. Take care

however, that water stored in that quantity will not stay fresh for long. You

will need to circulate, sanitize and filter it the same as the swimming pool.

Recently I have been specifying systems where the water storage will make use

of the Pool technique systems and be switched in for an hour or so when the

pool has been cleaned.

Second

question on sanitization.

The DDASS

will not accept a salt system, there is no Norm for that and they will require

you to change if you want to be registered. Hence you are obliged to consider a

chlorine direct system. I recommend that an automatic regulation system would

be the best for you, which are in effect removing the problem of marinating

your pool from your weekly chores as well as keeping a constant and expert eye

on the Pool’s Chlorine and pH levels. With nearly ever other system there is

work to do, testing and dosing. With the Pool controller, there is nothing to

do.

Your next

question how much water is used during a backwash. Well an interrogation of the

figures should reveal the clue. If your pool is 10 x 5 x 1.5 meters, flat

bottom than that will be 75 cubic meters of water. To comply with DDASS norm

you must circulate that the entire contents of your pool every 3 hours. So your

pump and filter should be specified to provide at least 25 meter cub per hour.

So if your back washing for 30 seconds that should be 25,000 litres divided by

120 (30 second periods in one hour) and that would mean about 208 liters. If

you do that once a week (necessary with sand, - once a day if you want to

comply with the Norm) that would be 5,408 litrs over a 26 week swimming season.

As I said before (and in other threads), if you run a Salt/chlorine system you

may not eject this water to the storm water, it must be consigned to an

evaporation pond. If you running manual chlorine direct then your better off

with soak away, but if your using Automatic dousing then you can go ahead and

put the back wash on your garden as the chlorine levels are so low that no harm

will come of it. If you are using ‘Aqua Crystal’, then this quantity will be

down to 2,600 liters over a 26 week swimming season which is half of the above.

An additional benefit is that the water in your pool will be 35 times cleaner

than with sand. That is: sand will give you 35-micron filtration – this is a

particle of dirt you can almost see. Aqua Crystal will give you 1-micron

filtration – this particle that is so small that it includes everything; all of

the known undesirable pathogens; as well as scrubbing the water for ammonia and

phosphates, none of which you want in your water. This is one spectacular

result, - really clean water.

I hope that

I have made the distinction adequately between Filtration and Sanitization. If it’s

not clear then perhaps I can put it like this.

If you can imagine

that the pool is filled with brand new ping pong balls. Over time with the

wind, dust and people in the pool, the ping pong balls become black and there

is many other ‘things’ in there with the ping pong balls. Filtration is a

system where all of the stuff which is not ping pong balls gets taken out of

the pool. Sanitization is a process where the ping pong balls a cleaned white

again. Maybe this is an over simplification, but the point needs to be made

very clearly, that EVERY pool, whether, domestic or commercial needs BOTH

systems. And they should be adequate for the size of the pool. This is

definitely not the place the save money on the pool build, nor is it the place

to add on something later. You should have a good filtration and sanitization

system from the beginning. Not to do so puts your health and that of other

swimmers at risk unnecessarily, as these do not cost the earth. Good systems

are affordable, what is in short supply in France it seems to me, is good

advice.

I hope that

this has been helpful.

 

Andrew

[Frank]

Thanks Andrew.

I suspect it may be a little more costly than I had hoped but the advantages of bein able to re-use the water on the garden is of benefit as is the "really clean water", yhanks again for an informative reply.

Probably have many more questions by the time I'm up and running

 

Phil.

 

 

[Poolguy]

Jetlag

If you want to chat about the options to get you problem solved than I am happy to help.

PM me with your contact details and we can chat about what to do.

If I can help I will.

Andrew