Appreciate your comments on the way we operate our pools

[JUCA]

We would appreciate to receive your comments on the way we operate our pools, particularly the club pools. We are learning a lot in this site and that is a good opportunity to demonstrate our gratitude for that wonderful assistance.
Our experience is that the key product to a healthy pool is bleach and the focal point to treat is the filter, since the filter area is more than one thousand the pool’s area. There are many possibilities to form colonies of algae, bacteria and other microbes in the volume of the sand inside the filter. And the quick way the algae growth in the pool when the chlorine goes to zero ppm, even when we treat the filter sand with bleach, is an evidence that they are still there.
We treat our club pools with bleach, supplemented with baking soda, chlorine acid, calcium chloride, sodium and cyanuric acid, the last under the form of dichlor. Before the presence of CYA we used sodium bisulfite when the chlorine was 5 ppm or over. Now we don´t consider necessary to limit the chlorine to 4 ppm.
The addition of bleach is done each day only at night, after we finish all activity, with the intention to have not TC higher than actual during the period of the use of the pool and, additionally, give a small shock. Although we have diaphragm pumps, additionally we opt to concentrate the treatment ounce daily at night to have a minor shock each night. Additionally, in the middle of the week, during the lunch period, we treat each filter with bleach (added in the pre-filter), kept into the filters during 30 minutes and, backwash the filers to the sewage.
We backwash the filters to the sewage two times per week and our preference is Monday and Friday. The water consumption is 6% of the volume of the pools per week, substantially with backwash and swimmer´s carried out. This means that the turnover water inventory is approximately 17 weeks or four months. We use this date to estimate the CYA content and calculate the dichlor to be add to stay between 10 and 20 ppm. We did not measure the CYA content. Our intention with this level is cut the presence of trichloramine by 50% and HClO by more than 90%, avoiding higher number because the impact in the shock level necessary to kill Bill.
We maintain the TC between 2 and 4 during the day , but TC goes to 6 after addition of bleach at night, pH at 7.6, TA between 80 and 120, CH above 250 and CYA between 10 and 20 ppm. The average consumption of chlorine in the club pools is 3 ppm per day. Before the treatment of the filters with bleach the average consumption of chlorine in the club pools was 5 ppm per day. The daily average frequency at the two principal pools is over 100 person per pool, from Monday to Saturday (at midday).
We use TC and not FC in order to simplify the frequent analysis and because we don´t have easy access to FC kit analysis. We measure the FC when we are trying to reduce the chloramines, as in the case of UV treatment.
The temperature of the two larger club pools is maintained between 86º F and 88º F and, the others two between 90º F and 92º F (hydrotherapy). The private pool is not heated and its temperature is estimated around 77ºF.
We use oxalic acid to clean the borders of the pools and the deposits, probably ferrous compound. Calcium chloride is used to precipitate calcium oxalate. In the process the pools became turbid and we backwash to the sewage, accelerating the process by adding clarifier into the pools. Weekly, at Saturday, we shock the pools, doubling the addition of bleach soda.
We try to maintain in our club pool´s a dynamic (measured at the entrance of the water in the pools) ORP minimum of 700 mv. We are now adding a UV in the 12000 gal pool, trying to reduce the chloramines presence during the day. The experience with UV is small (some days) but shows a reduction in the chlorine consumption and consequently reduction in the chloramines production. We tried hydrogen peroxide but this compound destroyed very quickly the HClO and gave us an headache with immediately growth of algae. We are using the CYA in the indoor pools with the purpose to reduce the complains about the irritation of eyes and skin with great success (we believe through the reduction of HClO and trichloramine). Apart from that, we maintain a air exhaustion system with a minimum capacity of six times the volume of the airspace pool. We use filter bag with 1mm mesh (when new) to reduce the amount of skin and other particles present into the pools - the bag filter is in parallel to the sand filter.
In our private pool we use calcium hypochlorite and we add only one time per week through the skimmer, using around 7 ounces per week. In this pool the TC varies between 10 (after we add hypo) and 5 (just before). Interesting is that when we introduce the practice of deep treating the filter with concentrated hypo, the consumption of chlorine drop to 1 ppm per day that is approximately the number that you mention that Janet (user name Aylad) obtained using 80-90 CYA. But we are using between 10 and 20 ppm of CYA. This pool receives directly sun light during 50% of the day. After we introduce the filter treatment with bleach we eliminate the brush since there is no more presence of algae. It is necessary only clean the debris in the bottom of the pool and clean the borders with oxalic acid.


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1) 40000 gal indoor ceramic club pool, 50´x 25´,2HP, sand filter, bag filter, 5 HP titanium heat pump.
2) 12000 gal indoor ceramic club pool, 26´x 16´,3/4HP sand filter, bag filter,5 HP titanium heat pump.
3) 4000 gal indoor ceramic club pool, 12´x 10´, 1/2 HP sand filter, 5 HP titanium heat pump.
4) 2000 gal indoor ceramic club pool, 9´x 6´,1/4 HP, sand filter, electrical resistance heater.
5) 6000 gal outdoor ceramic private pool, 24´x 10´, 1/2HP, sand filter.

 

[chem geek]

Welcome to TFP!

Thank you for your extensive comments. Your maintenance basically sounds appropriate, though I would encourage you to at least double-check your assumptions about the CYA level by using an accurate test kit. When you get the CYA as low as you do, you want to be careful or else the active chlorine level can get higher pretty quickly -- of course, it's still far lower than a typical pool without CYA.

Our experience is that the key product to a healthy pool is bleach and the focal point to treat is the filter, since the filter area is more than one thousand the pool’s area. There are many possibilities to form colonies of algae, bacteria and other microbes in the volume of the sand inside the filter. And the quick way the algae growth in the pool when the chlorine goes to zero ppm, even when we treat the filter sand with bleach, is an evidence that they are still there.

Sand filters in high bather load pools are notoriously troublesome because you are right that they tend to not circulate well so there are dead spots where bacteria and algae can grow. This happens more in commercial/public pools because the higher bather load provides a lot more nutrients and also the flow rates tend to be higher through the filters in order to achieve turnovers in the larger pools, but faster is not better when it comes to filtration.

The average consumption of chlorine in the club pools is 3 ppm per day. Before the treatment of the filters with bleach the average consumption of chlorine in the club pools was 5 ppm per day. The daily average frequency at the two principal pools is over 100 person per pool, from Monday to Saturday (at midday).

The 3 ppm FC per day is fairly consistent with a bather load of 100 people in a 40,000 gallon pool. I scale the hot tub bather load rule of 7 ppm FC in 350 gallons per person-hour figuring about half that for pool load unless competitive swimming is involved. So that works out to around 100*(7/2)*(350/40000) = 3.1 ppm which is what you are seeing. The actual bather load portion is less since you have a baseline chlorine usage in your pools even with no bather load of probably 0.5 to 0.7 ppm FC per day at the higher temperatures of most of your pools. So you're actually doing quite well, at least after you cleaned your filter.

Calcium chloride is used to precipitate calcium oxalate. In the process the pools became turbid and we backwash to the sewage, accelerating the process by adding clarifier into the pools.

Why are you precipitating calcium oxalate? I don't understand. Are you saying that when you clean the borders with oxalic acid that the calcium in the pool precipitates with it? You've got more problems with deposits than we normally see. Are these slimy as with algae or biofilms or is it more of a stain as you are implying with iron? The fact that oxalic acid removes it does seem to point to some form of scale or metal stain.

We try to maintain in our club pool´s a dynamic (measured at the entrance of the water in the pools) ORP minimum of 700 mv. We are now adding a UV in the 12000 gal pool, trying to reduce the chloramines presence during the day. The experience with UV is small (some days) but shows a reduction in the chlorine consumption and consequently reduction in the chloramines production. We tried hydrogen peroxide but this compound destroyed very quickly the HClO and gave us an headache with immediately growth of algae. We are using the CYA in the indoor pools with the purpose to reduce the complains about the irritation of eyes and skin with great success (we believe through the reduction of HClO and trichloramine).

Hydrogen peroxide and chlorine are incompatible, as you found out. In fact, hydrogen peroxide can be used to neutralize chlorine and is sometimes used for this purpose in residential spas.

I'm glad that the low CYA in indoor pool approach is working for you. Technically, another way to deal with this is to target a low chlorine level with no CYA of around 0.2 ppm as with the German DIN 19643 standard low end with ozone, but that is very difficult to maintain everywhere in the pool where local demand can use up that chlorine. CYA acts as a chlorine buffer so you get the best of both worlds -- a higher FC to have ample chlorine to not run out locally while having a low active chlorine level that minimizes nitrogen trichloride production from the oxidation of bather waste. This was all very theoretical (as I wrote about in this thread) so I'm glad I'm starting to see a few pools put it to practical use and working out. Way too few to say it's proven, but encouraging nevertheless.

Interesting is that when we introduce the practice of deep treating the filter with concentrated hypo, the consumption of chlorine drop to 1 ppm per day that is approximately the number that you mention that Janet (user name Aylad) obtained using 80-90 CYA. But we are using between 10 and 20 ppm of CYA. This pool receives directly sun light during 50% of the day. After we introduce the filter treatment with bleach we eliminate the brush since there is no more presence of algae. It is necessary only clean the debris in the bottom of the pool and clean the borders with oxalic acid.

Your 1 ppm FC per day with your outdoor pool with low 10-20 ppm CYA is puzzling, even accounting for a low FC that you probably keep at around 2 ppm or so. I've never seen that low a chlorine demand during the day with that low of a CYA. What is the FC level you are maintaining? Maybe you've got something else in the water shielding UV. I note that it's a smaller pool at 6000 gallons though I'm not sure why that would make any difference.

By the way, where are you located? There might be some decent filter options for you that could prevent some of the issues you've got with sand. Some recycled crushed glass filters do a better job. You could also look into adjuncts such as Fiber Clear that could be added for improved filtration that might cut down some organic load feeding the bacteria/algae in the sand, though really replacing the sand with a superior filtration medium is a better approach (though obviously more costly).

 

[JUCA]

chem geek wrote:
Why are you precipitating calcium oxalate? I don't understand. Are you saying that when you clean the borders with oxalic acid that the calcium in the pool precipitates with it? You've got more problems with deposits than we normally see. Are these slimy as with algae or biofilms or is it more of a stain as you are implying with iron? The fact that oxalic acid removes it does seem to point to some form of scale or metal stain.


Daily we clean the pools´ borders with oxalic acid. But annually, when we don´t empty the pool, we do the same with the walls and the botton of the pool, because they decame with dirty aspect, caused by a gray deposit. The only way we get sucess in removing the deposit in the botton and the walls it was brush with oxalic acid, what means a lot of oxalic acid into the water. In order to avoid any effect of this presence, we adds calcium chloride to precipitate oxalic acid in the form of calcium oxalate.

chem geek wrote:
I'm glad that the low CYA in indoor pool approach is working for you. Technically, another way to deal with this is to target a low chlorine level with no CYA of around 0.2 ppm as with the German DIN 19643 standard low end with ozone, but that is very difficult to maintain everywhere in the pool where local demand can use up that chlorine.

In the beginning of the operation we try to operate under 2 ppm TC. It was a crase period, with various periods without chlorine and dirty water to be clarified. We moved to range 2-3 ppm TC with good control of the chlorine presence but with many complains about smell, irritation of skin and eyes that gave us imput to go to 3-4 range. The number of complains decreasedbut still not confortable. Because of your work THE POOL WATER CHEMISTRY and others seen in TFP we conclude that with a small presence of CYA we could decrease the agressiviness of the HClO, reduce the presence of trichloramines and still have chlorine associated with CYA and available when necessary. Now we change our range to 3-5 ppm TC. We are just now applying UV in one of the pool and we know that the consumption of chlorine has dropped but we don´t know how much.

chem geek wrote:
By the way, where are you located? There might be some decent filter options for you that could prevent some of the issues you've got with sand. Some recycled crushed glass filters do a better job. You could also look into adjuncts such as Fiber Clear that could be added for improved filtration that might cut down some organic load feeding the bacteria/algae in the sand, though really replacing the sand with a superior filtration medium is a better approach (though obviously more costly).

We live in Rio de Janeiro, Brazil. As long as we know, the filter available here is sand filter and we thing it is doing a good job.
The problem as you mention is the amount of organic matters in club pools. We have gained experience with this filter and we consider dangerous to change.

Thank you very much for your quick and allways consistent reply

 

[JUCA]

chemgeek wrote:
Your 1 ppm FC per day with your outdoor pool with low 10-20 ppm CYA is puzzling, even accounting for a low FC that you probably keep at around 2 ppm or so. I've never seen that low a chlorine demand during the day with that low of a CYA. What is the FC level you are maintaining? Maybe you've got something else in the water shielding UV. I note that it's a smaller pool at 6000 gallons though I'm not sure why that would make any difference.[center:2gnl6ghp][/center:2gnl6ghp]

Our FC , as long as we verified (what is not frequently), is pratically the same as TC. The average use of this pool is two addult per day. In the private pool, it varies from 10 to 5 ppm. Our guess is that the strong treatment of the filter in our pool has created an environment with very low level of organic matter.

 

[chem geek]

There are plenty of people using all kinds of filters, having different bather loads, fresh fills of water, etc. that don't see the kinds of low loss in sunlight that you are seeing, at least at such low CYA levels. I'm not questioning why the loss got lower after you treated the filter, but losses due to organic matter would be seen overnight as well as during the day (especially if you ran your filter at night for an overnight loss test). It's not having a larger daytime loss that is the mystery, but I've been thinking more about it and running some calculations and having only 50% exposure does help quite a bit, though still not as much of a benefit as you are seeing. You are going from 10 ppm to 5 ppm so with your 1 ppm FC per day you are adding chlorine around every 5 days or so. This is a daily chlorine loss of around 13% per day. With only half sunlight exposure and 10-20 ppm CYA I could understand perhaps 25-30% losses, but just call yourself lucky and be thankful.

Just so you know, having 5-10 ppm FC with only 10-20 ppm CYA is going to be harsher on your skin, swimsuits, hair, etc. than if you were at a higher CYA level. 5 ppm FC with 20 ppm CYA is equivalent to 0.13 ppm FC with no CYA, but 10 ppm FC with 10 ppm CYA is equivalent to 1.4 ppm FC with no CYA. You already saw how the air quality improved through use of a small amount of CYA in your higher bather load pools, but for your own pool which is lower in bather load you could use a higher CYA level to make the chlorine less harsh. I assume you are using a good turbidimetric test kit for testing CYA and not using test strips which are very unreliable for testing CYA levels.

 

[JUCA]

You are right that there is no justification to use of CYA under 30 ppm in an open pool. Our reasoning it was that with 10 ppm CYA we were equivalent of 1.4 ppm FC without CYA in the worst condition, and that before the use of CYA it was normal to have 2 to 3 ppm.
The consumption number that we gave you iws the one that we received from the pool´s boy. As it is so different that you suppose is normal I will recheck and we´ll inform you after a period of evaluation.
Our titulometer measure only a minimum of 30 ppm. The number betwwen 10 and 20 ppm is done by estimation the loss of CYA with washing. We are trying to find a tool is minimum of 10 ppm.

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1) 40000 gal indoor ceramic club pool, 50´x 25´,2HP, sand filter, bag filter, 5 HP titanium heat pump.
2) 12000 gal indoor ceramic club pool, 26´x 16´,3/4HP sand filter, bag filter,5 HP titanium heat pump.
3) 4000 gal indoor ceramic club pool, 12´x 10´, 1/2 HP sand filter, 5 HP titanium heat pump.
4) 2000 gal indoor ceramic club pool, 9´x 6´,1/4 HP, sand filter, electrical resistance heater.
5) 6000 gal outdoor ceramic private pool, 24´x 10´, 1/2HP, sand filter.