Minimum Pool Maintenance This Year! Why?

[organicdog]

For the first time in 24 years I emptied my pool and power washed the entire concrete surface of the pool. For the rest of the season, after refilling, I did not have to add algecide, backwash, shock, or add DE. Only added chlorine tabs as needed. Can anyone tell me why? Will I be able to replicate this next year? Thanks, Herb

[duraleigh]

Can anyone tell me why? Will I be able to replicate this next year?

In a nutshell, you held adequate chlorine levels (through use of the tabs) in your pool all year. Algae simply does not grow in a pool with adequate chlorine.

Can you repeat it? Of course, but not likely by doing EXACTLY the same thing. Use of the pucks has probably elevated your CYA levels to a point where you will require much more chlorine than you did this year. Nonetheless, if you can get your CYA levels back to this years' starting point, then you can repeat your regimen.

You should test for CYA in the Spring (assuming your about to close) and bring CYA levels down if you plan to continue the use of pucks.

[floridapooltech]

Can anyone tell me why? Will I be able to replicate this next year?

In a nutshell, you held adequate chlorine levels (through use of the tabs) in your pool all year. Algae simply does not grow in a pool with adequate chlorine.

Can you repeat it? Of course, but not likely by doing EXACTLY the same thing. Use of the pucks has probably elevated your CYA levels to a point where you will require much more chlorine than you did this year. Nonetheless, if you can get your CYA levels back to this years' starting point, then you can repeat your regimen.

You should test for CYA in the Spring (assuming your about to close) and bring CYA levels down if you plan to continue the use of pucks.

Usually, you can run your pool using the tabs during the spring/summer without worrying about CYA levels exceeding recommended levels, then when fall comes around, use only liquid chlorine (no tabs) in the pool until the next spring which will allow the CYA levels to come back down, allowing you to repeat the process again without worrying about high CYA.

[James Watson]

People need to be careful about using tabs. The cyanuric acid can build up very quickly. Using nothing but tabs is usually a bad idea. Tabs need to be used in moderation and cyanuric acid needs to be watched carefully when using tabs. Cyanuric acid should be tested at least once a week when using tabs.

[duraleigh]

Using tabs without testing and monitoring your CYA level carefully is not a good plan. As James Watson said, the CYA can build up very quickly rendering your normal dose of chlorination pretty ineffective.

In a manually chlorinated pool, I think around 60ppm is as high as you should allow.....up to around 80ppm in a pool with an SWG.

[Allen G Myerson]

Usually, you can run your pool using the tabs during the spring/summer without worrying about CYA levels exceeding recommended levels, then when fall comes around, use only liquid chlorine (no tabs) in the pool until the next spring which will allow the CYA levels to come back down, allowing you to repeat the process again without worrying about high CYA.

The cyanuric acid should start out at at least 20 ppm and go no higher than 60 ppm. Therefore, you really have only 40 ppm of room to work with. Assuming 2.4 ppm of chlorine use per day, the cyanuric acid will rise by 1.44 ppm per day from using only tabs. That means that one could only use tabs for about 28 days before needing to switch.

However, if one used 90 % liquid chlorine and 10 % tabs, then they could go about 278 days before hitting 60 ppm.

In addition, this assumes that their cyanuric acid is at or lower than 20 ppm to start with. Most people start with higher cyanuric acid levels.

Furthermore, the chlorine in the tabs is very acidic, which requires the addition of continuous amounts of pH increaser or alkalinity increaser.

swimnsave's advice is designed to sell trichlor, pH increaser, alkalinity increaser, algaecide, phosphate remover, clarifier etc. and not to actually save anyone money as their name implies.

[floridapooltech]

1. Assuming 2.4 ppm of chlorine use per day, the cyanuric acid will rise by 1.44 ppm per day from using only tabs. That means that one could only use tabs for about 28 days before needing to switch.

Where are you coming up with this figure? There is no way to judge exactly how much rise per day in CYA. Every pool is different. You are also not accounting for rain, splash-out, evaporation, etc. Your answer on this is completely wrong.

2. Furthermore, the chlorine in the tabs is very acidic, which requires the addition of continuous amounts of pH increaser or alkalinity increaser.

swimnsave's advice is designed to sell trichlor, pH increaser, alkalinity increaser, algaecide, phosphate remover, clarifier etc. and not to actually save anyone money as their name implies.

The acid in a trichlor tab is not sufficient enough to declare a change in pH and alkalinity. Algaecide will not be required if you keep chlorine in your pool as algae will not grow in a properly sanitized pool. Phosphate's are completely irrelevant regarding this issue as well as clarifier. Where do you guys come up with this? rather funny. Also, since the OP most likely lives in an area we don't service with chemicals, how would this benefit us to give them wrong information? Also, as our name implies, our prices are in-fact the lowest in the nation.

[Allen G Myerson]

A 1 to 1.5 ppm per day increase in cyanuric acid is very realistic when using nothing but tabs.

The acidity of tabs will cause a continuous decrease in pH and TA. The chlorine in the tabs is very acidic.

[floridapooltech]

A 1 to 1.5 ppm per day increase in cyanuric acid is very realistic when using nothing but tabs.

The acidity of tabs will cause a continuous decrease in pH and TA. The chlorine in the tabs is very acidic.

Sodium Hypochlorite (liquid chlorine) raises pH, requiring the addition of acid
Calcium Hypo (granular) raises pH, requiring the addition of acid
Lithium Hypo (granular) raises pH, requiring the addition of acid

Dichlor is pH neutral

Chlorine Gas (gas) lowers pH, so bicarb is required (baking soda)
Bromine (granular, tabs) lowers pH, bicarb is required (baking soda)
last but not least...
TRICHLOR (granular, tabs) lower pH, bicarb is required (baking soda)

The change from trichlor is very limited at 2.8-3.5 ppm in a 1% solution.


Trichlor tabs contain 90% availabale chlorine, leaving only 10% for CYA and other additives. This being said, if the pool used the 2.4 ppm per day chlorine as you claim, then 10% of that would be 0.24 ppm CYA. leaving you with 160 days before a 40 ppm increase would have taken place, well within the spring/summer I claimed. Also, that does not account for the water loss/replacement which will lower the CYA levels even further!!! Also, that is if CYA took account for 100% of that 10% trichlor not taken up by chlorine.

[chem geek]

Here is a little info you may find useful before posting wrong info...

Sodium Hypochlorite (liquid chlorine) raises pH, requiring the addition of acid
Calcium Hypo (granular) raises pH, requiring the addition of acid
Lithium Hypo (granular) raises pH, requiring the addition of acid

Dichlor is pH neutral

Chlorine Gas (gas) lowers pH, so bicarb is required (baking soda)
Bromine (granular, tabs) lowers pH, bicarb is required (baking soda)
last but not least...
TRICHLOR (granular, tabs) lower pH, bicarb is required (baking soda)

You are neglecting the fact that chlorine usage/consumption is an acidic process and are only considering the pH change upon addition. When chlorine (hypochlorous acid; a weak acid) oxidizes ammonia or organics or when it breaks down in sunlight, it produces acid (hydrochloric acid; a strong acid). This is described technically here.

Hypochlorite sources of chlorine (chlorinating liquid, bleach, Cal-Hypo, lithium hypochlorite) when accounting for the acidity of chlorine consumption/usage are close to pH neutral except for the "excess lye" in bleach and chlorinating liquid. Dichlor is net acidic. Trichlor is very acidic.

If the consumption/usage of chlorine were not acidic (i.e. if one just looks at the pH change upon addition of product ignoring chlorine consumption/usage), then starting with a pH of 7.5, TA of 80, and assuming just 1 ppm FC per day chlorine addition, the pH would rise to 7.92 in just one week, to 8.37 after 2 weeks, to 8.58 after 3 weeks, and 8.72 after one month. Of course, this simply does not happen. With 12.5% chlorinating liquid with a pH of 12.5 (implying around 0.25% "excess lye") and accounting for the acidity of chlorine consumption/usage, the pH after one month would rise only to 7.55. In fact, this is what happens in my own 16,000 gallon pool where I only need to add about 1-2 cups of acid every month or so and much of that need is due to carbon dioxide outgassing from the pool when it is open (I have a mostly opaque safety cover with the pool open 1-2 hours every week day and longer on weekends).

In order to compensate for the net acidity of the non-hypochlorite sources of chlorine, one usually has the TA be higher and this causes faster carbon dioxide outgassing which (by itself) has the pH rise so the net result is a more stable pH, though the TA will drop over time. This happens most readily with Dichlor, for example, where it's use in spas can have the pH be reasonably stable, but the TA drops over time and if the TA gets too low then the drop in pH over time is seen as well.

The rate of pH rise (or offsetting a pH drop from net acidic chlorine sources) is dependent on the TA level and the amount of aeration since this is what determines the rate of carbon dioxide outgassing which is effectively removal of carbonic acid from the water. Pools are intentionally over-carbonated to provide a pH buffer and to protect plaster surfaces. TA is not just a pH buffer, but a SOURCE of rising pH itself.

The amount of TA drop using different net acidic chlorine sources is completely predictable from the chemistry alone. I will use 30 ppm FC as an example (and for the pH calculation, with 80 ppm TA and 7.5 starting pH), so that's one month of 1 ppm FC per day or 15 days at 2 ppm FC per day. If using Dichlor, then this has the TA drop by 10.6 ppm and if there were no pH rise from carbon dioxide outgassing, the pH would drop to 6.84. If using Trichlor, then this has the TA drop by 21.2 ppm and if there were no pH rise from carbon dioxide outgassing, the pH would drop to 6.63.

As for using bicarbonate for not only raising the TA, but also raising the pH when using Trichlor, that is very inefficient as it would require a rather high TA level to keep the pH in balance by forcing more carbon dioxide outgassing. Instead, it is more usual to use pH Up which is sodium carbonate as that not only raises the TA, but the pH as well. If you were to use bicarbonate (Alkalinity Up) to compensate for the TA loss, then for the pH to get fully restored, about 37% of the carbonates in the water (including that added by bicarbonate) would need to be outgassed. If instead one were to use sodium carbonate (pH Up) to restore the TA, then only about 23% of the carbonates in the water would need to be outgassed.

Richard

[Allen G Myerson]

The 90 % available chlorine is based on a chlorine gas equivalent. It is not the actual percent of chlorine in the tabs. Here is the equation:

2C3Cl3N3O3 + 6H2O <> 5H+ + 3OCl- + 3HOCl + 2C3H2N3O3

That's 425 ppm Cl2 for every 258 ppm of cyanuric acid. For every 10 ppm chlorine added by trichlor, the cyanuric acid will be raised by 6 ppm.

For example: Adding 1 pound of trichlor to 10,000 gallons of water will raise the Chlorine by 11, the cyanuric acid by 6.7 and lower the pH by 0.59.

Dichlor is acidic. Adding 1 pound of dichlor to 10,000 gallons of water will raise the Chlorine by 6.6, the cyanuric acid by 6 and lower the pH by 0.25.

Bleach is mostly pH neutral when accounting for consumption. There is some pH rise due to the sodium hydroxide, but it isn't very much.

[floridapooltech]

The 90 % available chlorine is based on a chlorine gas equivalent. It is not the actual percent of chlorine in the tabs. Here is the equation:

2C3Cl3N3O3 + 6H2O <> 5H+ + 3OCl- + 3HOCl + 2C3H2N3O3

That's 425 ppm Cl2 for every 258 ppm of cyanuric acid. For every 10 ppm chlorine added by trichlor, the cyanuric acid will be raised by 6 ppm.

For example: Adding 1 pound of trichlor to 10,000 gallons of water will raise the Chlorine by 11, the cyanuric acid by 6.7 and lower the pH by 0.59.

Dichlor is acidic. Adding 1 pound of dichlor to 10,000 gallons of water will raise the Chlorine by 6.6, the cyanuric acid by 6 and lower the pH by 0.25.

Bleach is mostly pH neutral when accounting for consumption. There is some pH rise due to the sodium hydroxide, but it isn't very much.

Your chemical composition is actually incorrect.

Depending on the inert ingredients by the manufacturer, (common) chemical reactions are as shown:

C3N3O3CL3
(Trichlor)

+ 3H2O
(water

--->

3HOCL
(Hypochloris Acid)

+ C3H3N3O3
(Cyanuric Acid)

[Allen G Myerson]

At a pH of 7.5, about half of the hypochlorous acid will become hypochlorite and most of the cyanuric acid will be in the form of C3H2N3O3, which accounts for the 2.5H+ that I showed.

[Allen G Myerson]

232.41 grams of trichlor contains 212.718 grams of Cl2 equivalent, but only 106.359 actual grams of chlorine. The chlorine only makes up about 45.76 % of the trichlor. About 54 % of the trichlor is cyanuric acid.

[Allen G Myerson]

chem geek
As for using bicarbonate for not only raising the TA, but also raising the pH when using Trichlor, that is very inefficient as it would require a rather high TA level to keep the pH in balance by forcing more carbon dioxide outgassing.

I agree with you about the efficiency. However, my issue with using sodium carbonate is that it produces an unacceptable amount of cloudiness. It is also much more likely to combine with calcium and create a scaling or precipitation event. The locally high pH and carbonates can also cause other unwanted adverse reactions with metals etc.

Baking soda does not create any cloudiness and it raises the pH slowly and continuously. If you have the TA right, you can almost exactly offset the pH decrease caused by the tabs. This provides a much more stable pH instead of low pH followed by high.

Baking soda does not cost very much, and I think that the benefits far outweigh the slight cost advantage you would get by using the more efficient sodium carbonate.