Algae problem

[Burch family]

For the last 2 summers i have had bad algae growth on the bottom and some sides of my pool. Could this be due to my salt chlorintion system not working properly or just due to high summer temps ?. Is it ok to swim in the pool within a few hours if chemical shock treatment used to remove the algae ?

Thanks in anticipation

Colin

[Théière]

Hi,

It could be down to a number of factors, poor pool design/hydraulics, too smaller chlorinator etc. What make is your pool?

It is a fair bet that there is insufficient chlorine, how do you test your pool chemicals?

What are the chemical levels in your pool?

Do you use stabilised pool salt?

How do you choc your pool?

What size is your pool and what type of construction?

How long do you run your pump for?

What type of filtration have you?

Sorry for all the questions but they are needed.

[chem geek]

Though it could be one of many problems including ones implied above regarding circulation and filtration or having an undersized system or too low a CYA level, it's most likely that you are not maintaining a sufficiently high Free Chlorine (FC) level relative to your Cyanuric Acid (CYA) level.  Many saltwater chlorine generator manufacturers recommend 60-80 ppm Cyanuric Acid (CYA) but with only 1-3 ppm FC and that is not high enough to prevent algae from growing using chlorine alone.  You need the FC to be at least 5% of the CYA level, so 3 ppm with 60 ppm or 4 ppm with 80 ppm.  You can learn more by reading Water Balance for SWGs.

[Théière]

Of course I agree Chemgeek but lets see where we are now before getting to where we should be. Another pool I recently attended using dip strip testing CYA 30ppm was actually 80ppm which explained a lot and the ALK was 220ppm which is why the owner couldn't keep control. 

[IMG]http://i701.photobucket.com/albums/ww13/picturebouquet/IMAG0102.jpg[/IMG]

Two hours later:

[IMG]http://i701.photobucket.com/albums/ww13/picturebouquet/IMAG0103.jpg[/IMG]

And 24 hours later it was crystal clear ready for the guests.

[Burch family]

Thanks for your reply re my algae problem . How do i measure the cya level in the pool water ? I have dip strips to measure ph, alkalinity etc can i use similar kit to measure cya ? I have copied yourwater balance info sheet for future reference .

[Théière]

Sadly the dip strips are literally only a rough guide and cannot be relied upon, Ph is about the only thing they are reasonable at. A couple of years ago 3 suppliers gave me there strips to test and they were all pretty hopeless and CYA being quite important was one of the worst on a couple of pools my tester had them at 180ppm & 200ppm the strips showed 30-40 [:(] Half of the problem is the test for one thing can run into the one below and through it off plus the colour charts are sometimes so hard to tell apart. A good tester is worth its weight and will save money by letting you know exactly what's going on so you don't waste chemical and fuel running to the pool shops. The scuba + is a good little tester made by Lovibond one of the most respected names in testing.  There are single testers on the market, you can just buy a CYA tester and a simple titration test for ALK the old favorite DPD1 for free chlorine and DPD3 for total chlorine would get you through but the total of all these would probably be higher than the Scuba +. Without the water figures you are really just guessing.

[Burch family]

Thanks for your reply regarding my algae problem .

The pool is mainly maintained by a friend who lives near our holiday home . I open and close the pool in late spring /autumn . The pool is mainly used by families who rent out house in July + Aug .

The pool was bought from Euro Piscine and is approx 8x4.5metres in size , 2metres depth at deep end . It is approx 3 years old built with concrete base and sides..

It has a salt chlorination filtration system [ Eurosel ]

The fitration is set for 10 hours/day in the summer months.

I have sometimes added up to 50kg of stabilised pool salt when the pool is opened in May/ June .

i use test strips to test alkalinity , chlorine? etc when i open the pool and i add ph + or - if needed .

if there is algae growth in July/ Aug our friend adds choc powders to cure the problem . Visitors are not happy if they cannot use the pool due to chemical treatment etc

Sorry can`t help with current chemical levels as we are not at the house again until 31 May .

I hope this extra info helps .

[Théière]

Ok Colin, understood. stabilised salt contains cyanuric acid (CYA) that is the stabiliser. Choc nearly always contains CYA too, you need CYA to protect your chlorine from burning off by the suns UV rays so it chemically bonds to your chlorine so although you measure "free chlorine" 90% isn't free at all its bound to CYA so there is very little active free chlorine around to deal with the algae (I am not too concerned with the exact % here just explaining the concept) CYA is also good as it reduces the chemical erosion on the titanium plates in the salt cell but to counter the green you will need more chlorine to choc the pool and also to run your chlorinator at a higher level (we don't know how high at the moment as we don't have accurate water figures. So we take a guess at around 70m3 you should add around 5 litres of javel from a brico shed plain unscented 9.6% @ 19euros for 20 litres. That will get used up quite quickly as it kills the algae so you must make regular additions of javel to maintain the high level until you have around 0.5ppm loss over night (test at dusk and retest before sun up. If that is too much trouble to ask of your friend just have them add a litre every 4 hours for the first day. there should be a dramatic change.

It may be difficult to test the chlorine level as it can bleach out strips and DPD1 but you can dilute the sample of pool water with the same of tap water, measure that and double the result.

If the budget will run to it buy a good quality tester to take with you it will save you money and headaches in the long run.

[Burch family]

Thanks Theirere for further advice.

Not sure if you mean i put javel in the pool at the start of the season instead of stabilsed salt or just when an algae problem arises ?

[Théière]

Sorry, I have gone ahead a little to quickly.  You need the stabiliser but only to a certain level, by using the stabilised salt each year and the choc pastilles/granules you are adding to that level but it doesn't get used up it just continues to build up to a point where you loose control of your pool.  The addition of javel is to sanitise your pool and kill the algae now, you need to increase the chlorinators chlorine output too as it is not keeping the chlorine level high enough to do the job effectively. Shocking a pool to kill the algae is not the addition of a product called choc, it is a process where you raise the free chlorine level to a much higher level than normal by adding chlorine and maintaining that level until the algae is dead.

If you need to add more salt use unstabilised salt such as water softener salt but really you need to test the water to find out what the levels are otherwise you will just suffer more frustration. Sadly test strips are too inaccurate to test for cyanuric acid level and alkalinity so gaining control of your pool will always be difficult without good test equipment.

[Burch family]

Theiere

Thanks for further good advice re water analysis+ treatment.

I will be opening up the pool next week for the summer season so i appreciate your technical advice and i hope to reduce the algae problem this year .

Colin