New Pool - Is Shock Required?

by Shannon Power
(Bowmanville, Ontario, Canada)

We have just filled a new 16 x 32 above ground pool with Tap water.

We have an auto chlorinator.

All pool levels are fine, except the chlorine, which is low.

Must we shock the pool, or will the chlorine come up on its own with the chlorine being added by the chlorinator?

(Temp outside is approx 75 Degrees.. temp of pool is currently 72 degrees)

I do not want to add any unnecessary chemicals.

Thanks very much.


Thanks for the question Shannon

It really depends on what the question means by "low". I had a question from another pool owner saying his chlorine was "too high". It was 4.0ppm, which is fine.

Normally, at pool start up, it's recommended that you do shock the pool to get the chlorine in there, but it's important on the kind of chlorine.

You need to get the stabilizer (cyanuric acid/CYA) up as well. Keep this between 30 - 50ppm and the chlorine between 1.5 - 3.5ppm.

The best chlorine for a start up is Dichlor. This is a stabilized chlorine as opposed to regular liquid or granular chlorine which is unstabilized.

For every 10ppm of chlorine added by Dichlor, you'll increase the CYA 9ppm.

You can then use Trichlor tabs for maintenance.

For every 10pm chlorine added by Trichlor, it will increase the CYA by 6ppm.

You then can use liquid or granular chlorine for weekly maintenance.

Be care when using Di and Trichlor as the CYA will rise and the only way to bring it down is to drain 1/3 - 1/2 of the water, refill, and balance the chemicals.

Hope this answers your question.

If you have any additional questions or would like to comment on your post, you can find it at the bottom of the Pool Start Up page and the Q&A page in the "Start Up/Opening A Pool" category:

Pool Start Up

Swimming Pool Questions and Answers

Have a fun and safe Summer.


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Opening My Pool, Shocking, And Swimming

by Janet
(Dallas, TX)

We just opened our pool last week and shocked it. The pool chlorine is up pretty high. I know it's over 15ppm. I was wondering how long before we can swim in the pool.

My kids really want to go swimming and I need to know.



Thanks for your question Janet

After opening your pool and doing a pool shock, you normally want to wait until the pool chlorine level is down between 1.5 - 3.5ppm.

This should take a few days with the Sun doing most of the work to get rid of the excess chlorine.

Adjust Your Swimming Pool Chlorine

Swimming Pool Chlorine

If you need to use the pool quickly there's a couple of options. You can drain 1/3 of the water out which will dilute the pool water but this might cause the other chemical readings to go off.

Swimming Pool Chemistry

Swimming Pool Tips

You can also use a product called Thiosulphate which is a chlorine neutralizer. You can follow the directions on the container.

I don't recommend using Thiosulphate too often as I've found with the YMCA pool and hot tub that it tends to mess up the water if used to often.

Hope this helps and good luck with your pool


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Chlorine Added, Now Shock?

by Liz Peters

I have a brand new 15' x 42" above ground plastic pool. I filled it with water from the garden hose.

Put 2 1" chlorine tablets in the filter (which has a built in chlorine dispenser).

What is next? Do I add Shock?

Thanks for the question Liz

I'd encourage you to get a Taylor FAS-DPD K-2006 pool test kit or you can take a sample of pool water on a weekly basis to your local pool store for analysis.

Pool Water Testing

Water Testing Kit

I'd also like to have your complete chemical readings: Chlorine, CYA (cyanuric acid/stabilizer), pH, Alkalinity, Calcium Hardness, and Metals (iron and copper). This would help in case anything else is too far off.

I will assume with your fill water that there's no chlorine or stabilizer (cyanuric acid/CYA). You want to shock the pool with Dichlor. This is a stabilized form of chlorine that will chlorinate you pool and put CYA in it. You want to bring the CYA level to 30 - 50ppm. When this happens, you'll stop using Dichlor and start using regular chlorine.

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. The tabs also have CYA in them so it's important to test that on a weekly basis as well. There's no chemical to reduce the amount of CYA. The only thing you can do is a partial drain and refill.

Swimming Pool Chlorine

Pool Shock

Pool Chlorine

Chlorine Tablets

Pool Chlorine Tablets

If you don't get the CYA in the proper range, your chlorine will dissipate quickly. Also, the chlorine will not be effective if the CYA is either too high or low.

Get back to me with the other readings so I can take a look at them as well.

Hope this helps and have a great Summer.


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Floc Not Working

by Tori

I have a 30,000 gal pool. It has been unused for a year or two by previous owners. It's in ground with a vinyl liner. It has a sta rite cristal flo sand filter. I used a whole bottle of HTH floc last night, recirculated for 2 hours, and then let it sit for 12 hours. I have a film of brown patches cover the entire top of the water. Per my local pool store, my levels were the following.can you please help me. Saturation idx: 0.4 TDS: 500 CYA: 0 Tot chlorine: 0.1 Free chlorine: 0 Ph: 8 Tot alkalinity:106 Adj. total alk: 106 Tot. Hardness: 178 Salt: n/a Copper: 0 Iron: 0 Manganese: no Hazy: no Cloudy: no Green/black/mustard algae: no Slime/ mold: no

Hi Tori. Floccs don't work for clearing up a green/cloudy pool. They only cover up the problem. My F.T.A. Process for clearing up pools is the best in the world as evidenced by these before and after pics, along with video testimonies from customers that have used it. All of that information and more can be found in my eBook, How To Clear Up A Green Pool. It's the only method you'll need for clearing up and maintaining the perfect pool. It goes into details such as chlorine use, pH ranges, floccs, clarifiers, and more.

For those who require personal assistance I offer a 90 minute phone consult where all of your questions will be answered.

You can find the links right here:

Clear Blue Pool eBook
Clear Up A Green Pool eBook
Swimming Pool Consultation


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