My local outdoor pool may have problems. We're getting through lots of chlorine (trichlor), the combined chlorine is high, and the pool has a strong chlorine smell. We've gone from 0 CYA (pool had been completely emptied and refilled) to 85+ in about 6 weeks, even with regular dilution. Chlorine levels are normally maintained at 1.5-3.0ppm. The water is always clear, but I still don't think it's a happy pool. Am I getting in a knot over nothing? How high is too high for combined chlorine on an outdoor pool? All the guidelines seem to be written for indoor pools.
how to get rid of pool smell
- Thread starter loop_pea
- Start date
Welcome to TFP.
Start by reading Pool School on how to shock your pool. Shock is a process not a product. Then learn how to use the pool calc.
You need to get a good test kit (see my sig). If you're test numbers are coming from a pool store be suspicious of them. They are usually inaccurate, especially the CYA test.
Any CC's over .5ppm means you need to shock. The fact that you're using a lot of chlorine points to that as well.
You should stop using trichlor immediately and shock with liquid chlorine (bleach).
Post back any questions you may have. We can help you get past this.
Start by reading Pool School on how to shock your pool. Shock is a process not a product. Then learn how to use the pool calc.
You need to get a good test kit (see my sig). If you're test numbers are coming from a pool store be suspicious of them. They are usually inaccurate, especially the CYA test.
Any CC's over .5ppm means you need to shock. The fact that you're using a lot of chlorine points to that as well.
You should stop using trichlor immediately and shock with liquid chlorine (bleach).
Post back any questions you may have. We can help you get past this.
If CC is higher than .5 ppm, then you should shock. You need to shock - but you need to lower your CYA first.
Please post a full set of test numbers.
Also, have you started reading Pool School?
Welcome to the forum
Please post a full set of test numbers.
Also, have you started reading Pool School?
Welcome to the forum
Thanks for the quick replies! We have a good test kit - photometer for FC, TC and CYA, so I'm confident in that CYA number. I'm less confident of the TC results, because the DPD3 test seems to change with time when you're at higher readings (4.0 ppm and over). Check at 1 minute and you get one number, take the reading at 2 minutes (as per instructions) another number, and the number will then continue fall. If the number at 1 minute is higher, is that the right number? Or should I always use the 2 minute number? I guess both numbers tell me that CC is too high, so maybe I shouldn't worry about too high vs much too high.
I did read pool school before posting. There seems to be resistance to shocking the pool here in the UK where I am - dilution is recommended instead, but we're doing that and it doesn't seem to be enough on its own. In previous years I think they've run exactly the same system (it's a short swim season and pucks are easier to handle than bleach) without the same problems. So I'm wondering what's changed? Sand filter full of yuck? I know nothing about sand filters.
I have lots of numbers because we test 2 hourly, although the record sheet isn't in front of me, so I don't have an exact result.
Typical readings for the pool water are pH 7.6 though it did go upto 7.9 a few times earlier in the season (so I added dry acid), FC is maintained between 1.5 and 3.5 ppm and CC is now in the region of 1.4 or could be higher, depending on the DPD3 test.
Our make up water has pH 7.47, TA of 220 ish and CH about the same.
I did read pool school before posting. There seems to be resistance to shocking the pool here in the UK where I am - dilution is recommended instead, but we're doing that and it doesn't seem to be enough on its own. In previous years I think they've run exactly the same system (it's a short swim season and pucks are easier to handle than bleach) without the same problems. So I'm wondering what's changed? Sand filter full of yuck? I know nothing about sand filters.
I have lots of numbers because we test 2 hourly, although the record sheet isn't in front of me, so I don't have an exact result.
Typical readings for the pool water are pH 7.6 though it did go upto 7.9 a few times earlier in the season (so I added dry acid), FC is maintained between 1.5 and 3.5 ppm and CC is now in the region of 1.4 or could be higher, depending on the DPD3 test.
Our make up water has pH 7.47, TA of 220 ish and CH about the same.
Even if you drain and refill you will still have to shock the pool to get rid of the organics unless you could drain almost 100%. Since you have the rest of the kit and are fairly certain of the results you should try and get a FAS-DPD to supplement your kit.
Pool is now shocked. I have put in 10 litres of 14% bleach, which should take it to just 20 ppm, and will go back in the morning and test using a diluted sample. This is the level recommended on the pool calculator for my CYA level. But it's not the same as on the pool school CYA/Cl chart, which is higher. Is that level for clearing up algae? There's no visible algae in the pool. Anyway, it's done, and this was also the dosage recommended on the container!
I've had a look around, but I don't know where to get the FAS-DPD test in the UK. It is possible to get it here?
I've had a look around, but I don't know where to get the FAS-DPD test in the UK. It is possible to get it here?
It's the morning, and my test results are:
1:5 dilution
FC=2.11 * 5 = 10.55
TC=3.11 * 5 = 15.55
I'm not sure if you can do the TC test on a diluted sample and still get a valid result, but if you can, it suggests that I'm a long way from eliminating the combined chlorine. What next? I understand the principle of keeping the chlorine high until the overnight chlorine loss is zero, or close to zero, but since I don't have the accurate test for high chlorine levels, this is all a bit hit and miss. Also, we're very close to the end of the season, and I need to think about closing the pool down. I don't want to spend lots of money on chemicals only to end up with a green swamp anyway - I only have an old solar cover, not a winter cover, so I don't think I'm going to be able to maintain a chlorine residual in the pool over the winter (and it's only July now).
1:5 dilution
FC=2.11 * 5 = 10.55
TC=3.11 * 5 = 15.55
I'm not sure if you can do the TC test on a diluted sample and still get a valid result, but if you can, it suggests that I'm a long way from eliminating the combined chlorine. What next? I understand the principle of keeping the chlorine high until the overnight chlorine loss is zero, or close to zero, but since I don't have the accurate test for high chlorine levels, this is all a bit hit and miss. Also, we're very close to the end of the season, and I need to think about closing the pool down. I don't want to spend lots of money on chemicals only to end up with a green swamp anyway - I only have an old solar cover, not a winter cover, so I don't think I'm going to be able to maintain a chlorine residual in the pool over the winter (and it's only July now).
Kes
0
Hi Loop_pea, 10 litres of 14% bleach would increase your FC (according to my calcs) by 15.5 ppm, which doesn't get your FC up to the pool calc recommended shock level (22) for your cya. It's a shame you couldn't test FC shortly after adding the bleach last night. (I assume 'bleach' is liquid chlorine.)
If you're diluting your pool water on a ratio of one part pool water to five parts unchlorinated water then you should be multiplying your readings by 6, not 5.
I am not aware of a FAS/DPD test kit for residential pools available through retail outlets in the UK, although I have not searched for public/commercial pool kits. Maybe Teapot can help.
If you're diluting your pool water on a ratio of one part pool water to five parts unchlorinated water then you should be multiplying your readings by 6, not 5.
I am not aware of a FAS/DPD test kit for residential pools available through retail outlets in the UK, although I have not searched for public/commercial pool kits. Maybe Teapot can help.
Hi Kes, thanks for the reply, it's nice to meet another UK forum user!!
My numbers all have some degree of uncertainty. If I calculate the volume of the pool based on given measurements, I actually get 80,900 litres, rather than the 90,000 litres that I was previously told. I put 80,900 in the pool calculator. There was already a few ppm of FC in the water, and so that plus the 10 litres of sodium hypochlorite should have taken me to 22 ppm or very close. Of course now I am wondering if the pool dimensions that I was given are exact - I'll have to get the tape measure out at some point, I suppose.
The test was done with 8ml deionised water and 2 ml pool water - it was my carelessness that I wrote 5:1 when I meant 4:1 and multiply by 5. The pipette that I used isn't terribly accurate, so the error in the final result could be substantial, like more than several ppm. I did another test at 50:50 dilution in the evening (24 hours after first addition) and got 10.78 ppm FC.
I haven't been out this morning to test - the pool is 1 mile away, and I haven't decided on what to do next. Combined chlorine is still up, so I guess I'm not finished. However, I don't have any algae to fight, over the last week the pool was finally holding it's chlorine levels overnight, and I know there's a good chlorine residual in the water, so I'm hoping that time delay isn't critical - although I suppose I'll be losing more chlorine to sunlight at higher levels, and will have to make up for that at some point.
My numbers all have some degree of uncertainty. If I calculate the volume of the pool based on given measurements, I actually get 80,900 litres, rather than the 90,000 litres that I was previously told. I put 80,900 in the pool calculator. There was already a few ppm of FC in the water, and so that plus the 10 litres of sodium hypochlorite should have taken me to 22 ppm or very close. Of course now I am wondering if the pool dimensions that I was given are exact - I'll have to get the tape measure out at some point, I suppose.
The test was done with 8ml deionised water and 2 ml pool water - it was my carelessness that I wrote 5:1 when I meant 4:1 and multiply by 5. The pipette that I used isn't terribly accurate, so the error in the final result could be substantial, like more than several ppm. I did another test at 50:50 dilution in the evening (24 hours after first addition) and got 10.78 ppm FC.
I haven't been out this morning to test - the pool is 1 mile away, and I haven't decided on what to do next. Combined chlorine is still up, so I guess I'm not finished. However, I don't have any algae to fight, over the last week the pool was finally holding it's chlorine levels overnight, and I know there's a good chlorine residual in the water, so I'm hoping that time delay isn't critical - although I suppose I'll be losing more chlorine to sunlight at higher levels, and will have to make up for that at some point.
Kes
0
Yes, I've found about four UK posters so far. You say you are not familiar with the sand filter - I assume you are backwashing fairly frequently?
I usually dilute in parts of 50 ml a time, one 50 ml measure of pool water to n x 50 ml parts of our unchlorinated spring water, mix, then take a sample from that. The theory is that the magnitude of error is reduced, but we all know the difference between theory and practice.
PS Out of curiosity, what's the temp?
I usually dilute in parts of 50 ml a time, one 50 ml measure of pool water to n x 50 ml parts of our unchlorinated spring water, mix, then take a sample from that. The theory is that the magnitude of error is reduced, but we all know the difference between theory and practice.
PS Out of curiosity, what's the temp?
I would keep at it, if you continue to hit it hard you can have this cleared up in a week or so - just keep it at shock level. I'm assuming the pool is closed to swimming? You can test and add chlorine as often as hourly, to maintain shock level. Hitting it especially hard in the evening hours will be most effective.
It seems to me you are making progress. You do lose a small amount of accuracy with dilution but I think you are going to be fine as long as you keep the FC up.
It seems to me you are making progress. You do lose a small amount of accuracy with dilution but I think you are going to be fine as long as you keep the FC up.
Kes - I'm learning about the sand filter, although there's still a long way to go. Backwashing is happening regularly, daily when the pool is in use. It's a small sand filter, I gather that it may be undersized for the amount of use that the pool gets.
The temp of the pool today is about 74 F. We try to keep it between 78 and 82, although it did go higher at one point - the boiler has no thermostat and it took a while to work out what setting we needed to keep the temp steady.
I like your method of dilution, sounds like a much better idea than messing around with small quantities.
frustratedpoolmum - I was about to post when I saw your reply. Yes, pool is currently closed to swimming for reasons not related to chemicals unfortunately. We would like to extend the swim season, but need to have things under better control.
Today I added up the amount of chemical we have used over the season (8 weeks). 81 * 200g tablets and 3.35kg of dichlor. Eek! Does it sound like a lot to you, because it does to me. And that's not including the shock treatments (with unstabilised chlorine).
The temp of the pool today is about 74 F. We try to keep it between 78 and 82, although it did go higher at one point - the boiler has no thermostat and it took a while to work out what setting we needed to keep the temp steady.
I like your method of dilution, sounds like a much better idea than messing around with small quantities.
frustratedpoolmum - I was about to post when I saw your reply. Yes, pool is currently closed to swimming for reasons not related to chemicals unfortunately. We would like to extend the swim season, but need to have things under better control.
Today I added up the amount of chemical we have used over the season (8 weeks). 81 * 200g tablets and 3.35kg of dichlor. Eek! Does it sound like a lot to you, because it does to me. And that's not including the shock treatments (with unstabilised chlorine).
Yes, that does seem a bit excessive (especially considering the tablets) but then again I don't know how long the pool has been opened?
Hang in there, we're here to offer our virtual support.
Hang in there, we're here to offer our virtual support.
Everything is on hold. The tester has to go away for recalibration/checking as it's been throwing out some dodgy results (pH gives same readings when sample is obviously a different colour, and the reading changes if you take it again). I have only 1 DPD1 tablet left at this time, and am reluctant to buy more if the tester is AWOL. Found out where to buy a FAS-DPD test kit in the UK, but it's expensive, and in any case not in my possession yet.
Can I keep the pool algae free with no testing? Help!
Can I keep the pool algae free with no testing? Help!