Hydrogen peroxide H2O2 in swimming pools; how much how often?

General Discussion
1

hi Everyone -
I have just joined SF - I hope that you are all having an enjoyable summer; I have a question, though I wonder if Ill ever remember how to find this thread again and any answers.

I have a house I rent out; after doing the Saturday summer changeover my next guests arrived 30 minutes early and there first words were “You pools’ gone green” - after 8 sweating hours changing beds, hoovering, shouting at the septic tank and cleaning toilets, this wasn’t music to my ears.
“Its turquoise,” I said and " the sand coloured pool liner can enhance the turquoise in the water" but basically experience has taught me, guests who see a tinge of green in the pool, are difficult to persuade that the pool is blue and i panicked and put 1ltr of H2O2 for each m3 of water - 7.5ltrs in total and the pool went blue.
Unfortunately I know that also finishes off the chlorine and getting it all back onto chlorine is going to be difficult I have chlorine dosing pump-
Please any advice for doing this gladly received.

(detail: I have raised stabiliser levels from a pastille based chloe choc 10 days ago, I have phosphates that are high, despite lowering then, something that I put down to the surrounding vines being sprayed during the night allegedly with a phosphate powder)
But can anyone help ? How much peroxide is 30-50ppm - I make it 2.25ltrs but how often and for how long.

Is John Withall around ? He seems to understand!

Thank you for reading and any advice

2

7.5ltrs is around the figure for a 50m3 to get it to 30ppm, you can go higher. How often depends on how quickly it breaks down burning out organics.

3

Hi John

Many many thanks for your replies; yes it was pool shop advice to add H2O2.

“It would have been better to counter the CYA with a higher level of chlorine.” Is this still an option now that the H2O2 has depleted- I tested it with a tester strip 28hrs after adding it and the strip reading was indicating almost nothing.

Could I now add liquid chlorine? - to get back to using the chlorine dosing pump and as you mention, lower the Cyanic (?) acid- stabiliser?

My difficulty lies in having guests at the house - for the next three weeks -who have rented my house , and wish to use the pool. They definitely prefer a sparkling blue pool. Is there a way changing back to chlorine, whilst keeping the pool as clear as the peroxide makes it. And also having a very high chlorine pool for a couple of days isn’t really an option (though if it rains allay maybe Could get away with it.)

pH is good 7.0/7.1/7.2 - automatic dosing pump.

I have added a concentrated flocculant and the pump is off overnight, I will vacuum (obviously not vacuum but i don’t know the term for it) out the flocculant and dead dust off the bottom tomorrow morning. (can i do that through the glass filter? or straight to waste? I usually go to waste as the dust seems so fine)

and need to decide what to do - add chlorine or continue with H2O2.

Any thoughts or advice gratefully received.

Thank you

4

If you are vacuuming via the filter, scrunch up some cotton toweling ( your partner’s best is great but not for happy life!) And put these in the skimmer baskets. That will trap really fine particles but will clog quite quickly, (look for reduced suction) you may need several.
The key to going back to Chlorine is what is the CYA level and dip strips cannot accurately measure CYA.

5

Good morning

Just measured using MPS level using a test strip. No reading or very low.

Pool is blue, slightly cloudy due to the floculant I think.

Obviously no chlorine reading on free chlorine test strip ;

Ok/high Stabilizer

PH 7.2

TAC around 80/120

If I added 7.5 liquid chlorine can I start to get back to chlorine rather than H2O2 without risking the dreaded green tinge. -“ your pools gone green” .”turquoise surely sir?” Is still my guest. Tho it’s grey day at the moment and not very conducive for swimming.

Basically I need to drop the CYA

Thanks

6

Thanks for your reply-again!

So best to get water tested at a pool shop.

Before the weekend, pool shop test was as below- this was before the H2O2 was added, the Stabilizer was 127 mg/l recommended level to be 100.

Other readings were

TAC 90mg/l. Recommend. 90+
pH 7.3

Free chl. 21. Had choced it because of algal bloom

Chl comb. 0mg/l

Cal dur. 232. Recomnd 128-85

Phosphate 1mg/l. Recomnd. 0.2

I saw from another thread that you managed to reduce the Stabilizer over a couple of weeks, where they had the same problem of not being able to drain large volume and refil with fresh water Was that using liquid chlorine?

I have slight issue with their testing because for another time it had it tested, they gave my pH at 6.7. I went back checked the calibration at 4,7,9 and it was perfect and my pool pH reading was 7.1. I sometimes wonder if their machine needs recalibration.

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Aaaaaarrrggghh. I opted for a salt water system. I never need to use chemicals. It works brilliantly. Why do you all put yourselves through this nightmare?

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Jess, I comment later as trying to assist David.

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David ask for their calibration cert, see when it was last calibrated.
127 ppm CYA requires minimum chlorine level of 10ppm don’t panic, with that level of CYA the active sanitiser is still less than 1ppm if you had no CYA i.e. less than a commercial indoor pool. Going higher would be beneficial for knocking out algae and clearing the water quicker.
Recommend CYA level 30-50ppm (70ppm if a salt chlorinator)
TAC recommended 40-80ppm for vinyl lined pools 80-120ppm for tiled/plastered pools.
Phos 0-0.2 phosphate is algae’s caffeine!

10

Hi John

Many thanks for your reply.

I have had the water tested but saw your email about asking for the calib cert after.

Results are: (all mg/l)

TAC 105 -okay

pH. 7.3 - my reading was 7.2 so okay

Free Chlorine 0.1 - to be expected

Combined Chlorine 0.1

Calcium hardness - 236 ( we have hard water - will deal with this later)

Stabilizer 113 - down 10 since Friday probably (?) due to filling and baskwashing and vacuuming over the weekend.

Phosphate 0.5 down from 1.0 on Friday ( lowest level all summer - H2O2 helped I guess)

So…

“127 ppm CYA requires minimum chlorine level of 10ppm don’t panic”,

Can I add liquid chlorine to cover this? For a 75m3 pool- 75,000,000ml - would that be 7.5ltrs chlorine?

Leave overnight- no swimming?

Sorry I don’t understand this bit of your reply,I got a bit lost when you mentioned “active sanitizer “:

“with that level of CYA the active sanitiser is still less than 1ppm if you had no CYA”

“Going higher” -is that higher with the chlorine?- “ would be beneficial for knocking out algae and clearing the water quicker.”

“Recommend CYA level 30-50ppm” -this is quite hard to get down to just using my topup and backwash/ vacuum method. Would that excess chlorine help bring it down as well?

“TAC recommended 40-80ppm for vinyl lined pools 80-120ppm for tiled/plastered pools. “Mine is liner. And I am at 105

“Phos 0-0.2 phosphate is algae’s caffeine!” Agreed. I think H2O2 must have helped, maybe more H2O2 will kill it. ( I think it might be being increased by the vines being sprayed with phosphates around me. Apparently the spraying is nearly over. I have been using Bayrol Nyphos to lower the phosphate levels but they keep going back up. Very annoying and likely to have been a factor in producing “the dreaded green tinge”)

Also I have tested with Aquacheck Peroxide testing strips- water this morning was between 20-30 no units given, but ppm- I guess tho it doesn’t say.

( not quite sure what PMS that I tested earlier was!)

And yes thanks for the salt pool suggestion, I used to use that method of chlorine conversion here, was fine until it went wrong.

Thanks again!

Best wishes

11

Hi David,
Yes I would probably agree CYA down 10 probably due to filling and a bit from being oxidised out.

Phosphate down 0.5 doubtful H2O2 would effect it, however interestingly as it’s food for algae they actually consume it, often though they leave the byproducts of ammonia which causes a massive chlorine demand before you can get the free chlorine level up to normal levels.

7.5ltrs of chlorine (Brico shed eau de javel) is just the dose to give you free chlorine level of 10ppm which is not the shock level. Shock level would be 45ppm of chlorine (33ltrs)

Free chlorine is the measure of the chlorine in the water, not combined chlorine (chloramines). CYA binds to the chlorine reducing the loss of chlorine to sunlight. The actual active sanitiser in the water is hypochlorous acid and hypochlorite ions. We know from chemical tables of equilibrium chemistry (O’Brien 1972) that around 99.98% of the chlorine is bound to CYA producing a very low active hypochlorous/hypochlorite in the water so we add additional chlorine to produce a sufficient active hypochlorous/hypochlorite solution to kill algae and bacteria.

That means with 10ppm of chlorine in the water with 113ppm of CYA there is roughly the same active sanitiser level as a pool with 1ppm chlorine and 0ppm of CYA. An indoor commercial pool is unlikely to have CYA in the water but may have 3ppm of chlorine in the water. That is a very high level of active sanitiser roughly equivalent to you running your pool on 30ppm of chlorine with 50ppm of CYA!

The lack of understanding of this chemistry is rife from country to country and is only just being taken on board from peer reviewed chemistry of 1972. I am fortunate to have learned this from a chap known as ChemGeek, Richard Falk, to whom I am most grateful.

If you add more chlorine than needed some of the CYA will be slowly oxidised but this is way more expensive route than emptying and replacing the water. You really need a 50% water change, There are enzymes that can be added to the pool which eat CYA but results are variable and there must be absoutely no sanitisers present in the pool.

TAC, don’t worry abot 105ppm you just get the pH rising a little easier than with a level of 40-80ppm.

The peroxide 20-30ppm sounds right, I didn’t comment about the PMS earlier but I was puzzled as PMS is peroximonopersulphate another popular non chlorine product but not H2O2 glad you have got the correct test. You will not be able to use chlorine until the H2O2 level is near 0, if you do the H2O2 will just oxidise the chlorine out as it is a stronger oxidiser. That’s why I really do not like pool shops that sell this as a solution. Converting back means your pool can go swamp like for a bit and you’ll normally need plenty of chlorine to get rid of the peroxide remenant.

You can’t use a salt chlorinator as you rent the pool to paying guests it’s not allowed.

OK you must be bored to tears by now! :grin:

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12

You add salt, that’s a chemical, sodium chloride which is converted into chlorine just the same. You need to have CYA stabilser in the pool water or you’ll loose the chlorine to the suns UV which means your chlorine generator cell will be trying to work overtime to keep up with the loss of chlorine meaning a shorter cell life and they are expensive to replace.

Normally a salt chlorinator will cause a pH rise but this is dependant of the alkalinity of your local water supply. Some areas of France like mine have 280ppm of alkalinity, others 27ppm so one size doesn’t fit all and some constantly battle adding pH minus.

When I first came to France I worked on more salt pools than anything else and I began to loathe them. direct chlorine was far simpler and more effective and what I was more used to. As my knowledge of these units grew, I realised where customers were making mistakes or units were simply undersized for the job. Also the early units used to fail more often, built up calcaire easily and stopped working, they have improved over time but the water chemisrty is still the same and I have seen green swamps from Bio-UV, salt chlorinators, Chlorine galetts and direct dosing its down to testing and a bit of house keeping. Once the basic knowledge is understood it gets a whole lot easier.

France has a few rules on pools, some good some not and one of the main ones is you cannot have a salt chlorinator system on a pool that is used by more than one family i.e rented as in Davids case.

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That is a very interesting point, @Corona and well worth noting by anyone who plans to allow paying-guests to use their swimming pool.

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14

Dear John,

A most excellent reply, I am most grateful for all your expertise and er, yes I have a few questions.

To save you from them though, my understanding is that I should stick with H2O2 whilst I have guests; to avoid a green changeover between H2O2 and Chlorine, not with standing the fact there is too much Stabiliser and emptying 50 % and refilling is not an option so a changeover could not not be easily achieved.

If I continue with H2O2 level should be at 30-50 ppm.

For for a 75m3 pool, to raise the level would be 75ml water per ppm of H2O2? so to go from 25ppm to 50ppm I would require 25 x 75ml of H2O2? = 1.875 ltrs of H2O2. is my maths rubbish - i think it might be!

I thoroughly enjoyed your reply and am rereading it!

Best wishes,

15

Am I ten times out!

I would need 25 x 750ml H2O2 = 18.75 ltrs

16

Yes I would probably agree CYA down 10 probably due to filling and a bit from being oxidised out.* i got that bit right!*

Phosphate down 0.5 doubtful H2O2 would effect it, *I think it must have ben this, that the lowest its been all summer - when I add ore H2O2 and test the water I’ll report back! *however interestingly as it’s food for algae they actually consume it, often though they leave the byproducts of ammonia which causes a massive chlorine demand before you can get the free chlorine level up to normal levels. okay not great

7.5ltrs of chlorine (Brico shed eau de javel) is just the dose to give you free chlorine level of 10ppm which is not the shock level. Shock level would be 45ppm of chlorine (33ltrs) i realise that is a massive amour of chlorine, would it take a long time to dissipate (apologies wrong word ) before it was safe to swim?

Free chlorine is the measure of the chlorine in the water, not combined chlorine (chloramines). CYA binds to the chlorine reducing the loss of chlorine to sunlight. The actual active sanitiser in the water is hypochlorous acid and hypochlorite ions. We know from chemical tables of equilibrium chemistry (O’Brien 1972) love that paper … now anyway that around 99.98% of the chlorine is bound to CYA *I see the problem with the CYA now!- needs to be lower -as you explain below *producing a very low active hypochlorous/hypochlorite in the water so we add additional chlorine to produce a sufficient active hypochlorous/hypochlorite solution to kill algae and bacteria.

That means with 10ppm of chlorine in the water with 113ppm of CYA there is roughly the same active sanitiser level as a pool with 1ppm chlorine and 0ppm of CYA. An indoor commercial pool is unlikely to have CYA in the water but may have 3ppm of chlorine in the water. That is a very high level of active sanitiser roughly equivalent to you running your pool on 30ppm of chlorine with 50ppm of CYA!
*weird , but I think I get it… I have CYA, there’s nothing I can do about it, so I have to have a much higher chlorine ppm than a public pool , but not much of my chlorine is free, because there is so much CYA - *

The lack of understanding of this chemistry is rife from country to country and is only just being taken on board from peer reviewed chemistry of 1972. I am fortunate to have learned this from a chap known as ChemGeek, Richard Falk, to whom I am most grateful.sound like a most excellent man

If you add more chlorine than needed some of the CYA will be slowly oxidised Ah-ha the chlorine will lower the CYA part, that I hoped would be my savior but darn this is way more expensive route than emptying and replacing the water. You really need a 50% water change, *later in the year unfortunately * There are enzymes that can be added to the pool which eat CYA but results are variable and there must be absoutely no sanitisers present in the pool.and there are…

TAC, don’t worry abot 105ppm you just get the pH rising a little easier than with a level of 40-80ppm.got it

The peroxide 20-30ppm sounds right, I didn’t comment about the PMS earlier but I was puzzled as PMS is peroximonopersulphate another popular non chlorine product but not H2O2 glad you have got the correct test level seems to be around 25ppm 36hrs after adding approx 7.5 ltrs.

You will not be able to use chlorine until the H2O2 level is near 0, if you do the H2O2 will just oxidise the chlorine out as it is a stronger oxidiser stick with the peroxide for the next three weeks then . That’s why I really do not like pool shops that sell this as a solution. Converting back means your pool can go swamp like for a bit and you’ll normally need plenty of chlorine to get rid of the peroxide remenant. roughly , very roughly how much -50ltrs? and how long would that be unswimmable? - 3days ? 7 days ? 2 weeks?

You can’t use a salt chlorinator as you rent the pool to paying guests it’s not allowed. exactly

OK you must be bored to tears by now! :grin: nope very very enjoyable, thanks