by Jaro
(Ontario, Canada)

Chlorine is being rapidly lost by some chemical reaction - Please advise.

Pool: Concrete/plaster, 80 000 L = 21 000 US gal., Sand filter new – Hayward S244T, solar heating

Chlorine chemistry: HTH granular 65% Calcium Hypochlorite + 3” HTH pucks in Cl feeder

History of chem. parameters and chemical additions:

May 24 Start up 1pm, 7pm 1400g Cl

May 25, 10am: free Cl 1, pH 7.6, 1-3pm 3.7 L Muratic acid, 4pm 1400g Cl, 8pm 1400g Cl

May 26, 10am: free Cl 0.4, pH 7.0, Stab. 0, 1-3pm 1.75 kg Stab., 7pm 1400g Cl

May 28, 10am: free Cl 0, pH 7.0, 11am 1400g Cl, 10pm 1400g Cl, 10 pm 400g pH-Up

May 29, 8 am 400g pH-Up, 9am 600g Cl, 1pm test: free Cl 0, pH 7.3, Stab. 5

May 30 home test: 7pm free Cl 0.3, 10 pm free Cl 5, 2 hrs after 1400g Cl

May 31, 10am: free Cl 0, pH 7.1, 10:30 pm add 500g pH-Up

Thanks for the question Jaro and the readings

There's a few things that jumped out at me. First is the use of calcium hypo, then muriatic acid, then pH Up.

Calcium hypo is a good source of chlorine, but it has a pH level of 12. Each time you use it the pH will slightly increase. Then you're using muriatic acid to decrease the pH, then pH up to increase it. This is burning a hole in your wallet.

If you're having an issue with the pH jumping around, use liquid chlorine and keep the alkalinity between 80 - 100ppm. This will lock it in place. You can also use unscented bleach for chlorine. It's the same thing as pool chlorine, sodium hypochlorite, only about 1/2 the strength.

On May 25 the pH was 7.6. That was a good reading. If the next pH reading is around 7.4 - 7.8 leave it alone. Only decrease it if it gets above 8.0.

Next, you
can use baking soda or 20 Mule Team Borax to increase the pH. Baking soda is also used to increase the alkalinity, it's just how you apply it that matters if it hits the pH or alkalinity.

Anything called pH Up or Alkalinity Up is either sodium carbonate or sodium bicarb which is baking soda. Go to your grocery store and get a box of Arm & Hammer for 1/3 the price.

Swimming Pool pH Levels

Pool pH

Pool Alkalinity

Total Alkalinity

It seems the reason the chlorine isn't holding is you don't have enough stabilizer, cyanuric acid (CYA). The CYA needs to be between 30 - 50ppm. Use Dichlor and shock the pool. You should be able to get Dichlor chlorine at your local pool store. This will get the CYA into the pool.

Once you get a CYA reading of 30 - 35ppm, stop using Dichlor and go back to liquid chlorine for weekly maintenance. CYA reading should be between 30 - 50ppm. Your'e already using Trichlor pucks which is dosing your pool with CYA so you want to start low and work up from there.

Don't shoot for 50ppm CYA with the Dichlor, stop at 30 - 35ppm.

Be careful when using Dichlor as it can get out of hand quickly. For every 10ppm of chlorine added with Dichlor, you'll raise the CYA by 9ppm. For every 10ppm of chlorine added with Trichlor tabs you'll raise the CYA by 6ppm.

Shock at night then retest in the morning. Keep filtering 24/7. As the CYA starts to rise you'll notice the chlorine will hold longer. Remember to allow for 1 full turnover of the water before retesting.

If you make an adjustment then retest after an hour you're not going to get an accurate reading. A turnover is normally about 8 - 10 hours.

You're doing a great record keeping job. You're notating everything and looking for patterns. That's 1/2 the battle.


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Constant Low Chlorine Levels

by Ida & Tom

We have been experiencing many issues with our pool levels.

First of all it does not hold the chlorine proper levels even though we keep putting in tablets, liquid chlorine etc.

Secondly, the cyanuric acid is high at 140ppm and the phosphate level is at 500. We are always on the way to the pool shop to buy more chemicals.

Could you please give us an idea what to do to resolve this issue?


Ida and Tom

Thanks for the question

First, I'd like to have the rest of your chemicals readings:

Chlorine, pH, Alkalinity, Calcium Hardness, Metals (iron and copper), Total Dissolved Solids, CYA

It makes troubleshooting much easier and the process of clearing up your pool will go much faster. Without these numbers I'm just guessing at what the problem is.

The question says the chlorine levels are not holding at the proper levels. At what levels are you trying to reach?

The CYA is very high. The reason that the chlorine can't hold is because you would need to bring the chlorine up in proportion to the CYA.

Pool chlorine needs to be 7.5% of the CYA and the proper range is 30 - 50ppm.

The only way to reduce the CYA is to do a partial or full drain, refill, and balance the chemicals again.

You're probably going to need to drain 2/3 of the water and refill with fresh to get the CYA down to between 30 - 50ppm. Take out the chlorine tabs right away. You don't want to increase the CYA.

Now for the phosphates.

I recently answered a question from a lady in Chicago that has a big problem with phosphate remover.

High Phosphates Over 1000 & Cloudy Water

And these posts:

Swimming Pool Phosphate Level Over 1000

High Phosphate Levels And Low Chlorine Issue...

It's basically this:

Phosphates are food for algae, but, if you keep the chlorine level between 1.5 - 3.5ppm, the algae will be killed by the chlorine.

Good chlorine level = no algae or bacteria. It doesn't matter the level of the phosphates. I would advise you to NOT get a phosphate remover. It's an added expense and something your pool doesn't need.

You can have a phosphate level up to 1000 and it'll be fine. You don't need to buy any more chemicals. Just drain and refill, keep the CYA between 30 - 50ppm and chlorine between 30 - 50ppm.

Some items you can find the grocery store to balance your chemicals such as bleach, baking soda, and 20 Mule Team Borax.

If you could give me the chemical readings, we can go into a little more detail and get your pool up and running quickly.


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Do You Have To Use Chlorine Everyday?

by Gord

I have heard that you can just shock your pool once a week and not have to use chlorine, is this true?

What are the side affects of not using chlorine in your pool and just shocking it?

Thanks for your question Gord

I have heard of this before, but I'm really not a big fan of just shocking once per week, then not doing anything else with the chlorine.

Chlorine Demand

When I did my pool route in Arizona I would raise the chlorine level up a bit, when needed, to about 5.0ppm or so. This was to carry the chlorine level throughout the week until I could get back the following week. The CYA (cyanuric acid/stabilizer) must also match the chlorine level. By this I mean it needs to be in range, 30 - 50ppm CYA and the chlorine is 7.5% of that level.

A normal home pool requires the chlorine level to be between 2 - 4ppm and the CYA between 30 - 50ppm. If you bring your chlorine level up to a true shock of 10Xs the normal chlorine level, say 10 - 12ppm, you'll also need to raise the CYA. At a chlorine level of 10ppm, the CYA would need to be 75ppm. If you use Trichlor pool tabs. your pool CYA is being slowly added to the water. This will eventually raise the CYA, but too much and the chlorine sanitizing properties will be compromised.

There's too much of a fluctuation in the readings for the chlorine to do its job correctly. Granted, your chances of algae or green pool water would drastically decrease, but I think you'd be wasting more money than you're actually saving. Swimming pools aren't a "set it and forget it" proposition. It is called "pool maintenance" for a very good reason.

I would normally add either a pound or gallon of pool chlorine to my pools about every other week. This was even when the temperatures reached 105 - 110 degrees for weeks at a time.

If I did a shock every week, for every pool on my route, my chemical bill would be so outrageous it would have probably put my out of business. If you like to swim, as I hope most people do who visit this website, they'll need to wait longer to swim because of the high chlorine levels.

When you start getting over 6.0ppm your skin can become very itchy and dry due to the excess chlorine. Not to mention the red eyes. I would be very cautious of someone telling you that you can simply do something once with your pool, forget about it for a week, and it'll be o.k. No need to worry about it.

What I'm telling you is from years of real world experience, a pool route of 50 residential and commercial pools in one of the hottest parts of the country, Arizona.

Also the YMCA pool operator for the last 3 years. Everything on this site...I've personally done. From help with construction, to plumbing, to installation, to chemical readings, to cleaning, to ordering, billing, collecting, to whatever...

I've actually drained a pool 1/2 way, hung upside down with my uncle holding onto me, rewired and installed a new pool light when it was 108 degrees. Yeah. Fun times. I was a little younger and more flexible back then.

It's my opinion that the chlorine level should be kept between 1.5 - 3.5ppm, CYA 30 - 50ppm, and all chemicals tested once, if not twice per week. This is the tried and true method of taking care of pools. Many pool owners and pool guys have done this for years with much success. If it ain't broken, don't fix it.

Thanks again. I hope this helps and have a great and safe swimming season.


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