How Long Does It Take for Pool Chemicals to Work

Adding Chemicals to your pool should be done on some type of schedule but then there are times because of usage or work that make it impossible. In the event, of a pool water problem or you are just in a hurry and need to add chemicals, How long does it take for pool chemicals to work?

How fast Pool Chemicals work is dependent on the size of the pool, the pumping rate of the filter system & how much chemical is needed. 
Alkalinity takes 6-8 hrs. or a full turnover of the pool water
PH is 4-6 hours.
Shock Chlorine- at least 30 min.
Cyanuric Acid- one full turnover-then 5 days
Hardness-6 hrs.

The time frame for adding different chemicals to your pool will have variables that come into play. If you know them then you are in control of your swimming pool.

How Long Does It Take for Pool Chemicals to Work


How long you wait between chemical doses and applications depends on a few variables that you should already know about your pool. Variables like:

  • Size-The size and volume of your swimming pool are the keys to how long you filter your pool to recirculate and turn it over. To get the Volume of your pool take Length x Width x Average Depth = Volume
  • There are 7.5 Gallons of water in 1 cubic ft. So if your pool was 20 ft long and 17 ft. wide with 4ft at the shallow end and 8ft at the deep end that will give you an average depth of 12 divided by 2 equals an average of 6ft.
  • 20 x 17 x 6 =1440 x 7.5 = 15,239 gal.
  • Length times width gives you the surface area of the pool. Multiplying that by the depth gives the volume in cubic feet. Since there are 7.5 gallons in each cubic foot, multiply the cubic feet of the pool by 7.5 to arrive at the volume of the pool, expressed in gallons.


The turnover rate- is dependent on the size of the pump in the filtering system. Industry standards recommend a minimum target turnover rate of 6 hours and a minimum of 2 turnovers per 24 hours. The pool turnover rate is important for proper filtration. Not cycling enough water through the filter can result in swimming pool algae blooms, cloudy pool water, and water balance issue.

A complete turnover of the pool is somewhere in the ballpark of 6 hours. You can help with some chemicals by mixing the pool by hand using a skimmer that will help make it faster.

For Alkalinity AdjustmentsI would wait the turnover rate of around 6 hours before re-testing.

It’s been my experience that with Alkalinity measurements the more the soda ash is mixed the more dependable the readings. This follows true again with the PH adjustment. So take your time. Alkalinity adjustments with soda ash or with muriatic acid to lower it can seem to rise fast and then fall down just when you think that the readings are starting to stabilize and level off. If you don’t wait long enough then you’ll make it worse and will be ping-ponging the Alkalinity and PH.

Get a hold of one and then the other. Stabilizing Alkalinity to hold off using PH adjustment for 2 to depending on how big your pool is for 4 hours. The chemistry involved in Alkalinity is the base for other required chemistry to work off.

PH and Disinfection (chlorine) are dependent on the Alkalinity to be rock solid inside that 80-120 ppm for everything to click and this is where I recommend some time.

Total Alkalinity is a buffer or sponge that resists rapid pH change in pool and spa water. Without a proper buffer, pH can have rapid swings from high to low for little to no reason, throwing the pool chemistry out of whack.

PH Adjustment takes less time. Once the Alkalinity is in a state where the chemistry of the pool water is strong then the Ph chemical will act accordingly. A strong base can make the pool water pH extremely difficult to change. But a filter Cycle turnover rate is recommended.

But too much Alkalinity can also result in cloudy pool water due to suspended calcium carbonate. High pool alkalinity reduces chlorine effectiveness leaving the pool water without protection and allowing algae, bacteria, and other contaminants to grow.

It can also cause clogged filters, clogged heater elements, and reduced circulation, as a result, the clogging.

Keep the Alkalinity in the range between 80 ppm-120 ppm. Use a pool calculator or does on the pool chemical.

Using the dimensions of this pool 20 x 17 x 6 =1440 x 7.5 = 15,239 gal. and an Alkalinity of 80 ppm I determined that in order to bring the Alkalinity up from 80 to 100 ppm I will need approximately 4.5 lbs of Soda Ash.

Run the Filter on Recirculate and help move the water around with a skimmer pole.

Another tip– is to turn the effluent line heads in the pool directly down. This action with the filter running mixes the pool properly by pushing the effluent down toward the bottom center of the pool and creating a circular movement of the pool water.

None of this will work if you don’t own a reliable Test Kit like this LaMotte ColorQ Pro 11 TesTabs Digital Pool & Spa Chemical Water Testing Kit  The digital photometer measures the intensity of light, so no more matching colors to guess where your water levels fall on the chart. Take Testing seriously and you will see a big difference. 


How Long Do You Wait Between Adding Pool Chemicals?

All pool chemicals take their own time to mix and dissolve when added to pool water then changing the chemistry of the pool water but it all depends on the chemical’s active ingredients or strength and the volume of your pool ……………………………………………………….Read more

 Adding Pool Chemicals


Once a chemical establishes itself and it’s where it needs to be you can add the next one and balance the chemistry of the pool. The first should always be Alkalinity.

Alkalinity adjustment with Soda Ash – After 4-6 hours start testing again. Once you see the levels start to slow down and then stop, it may even stop sooner than later or it may take a little longer than move on.

PH- Then you can add the PH adjustment. With PH Plus and PH minus or with Muriatic Acid, I prefer to use when lowering PH. Be careful handling Muriatic Acid. It’s highly volatile but works well.

I’ll recommend about 2 to 4 hours to wait for re-testing PH. Some Pool Suppliers recommend a full cycle turnover which in this situation would be 6 hours but you’ll be able to see if it is still moving or fluctuating.

If you adjust PH up or down in small increments you might need even less time which is good because if there was a problem with Alkalinity then there’s a problem with PH and if there’s a problem with PH then there is a problem with your Chlorine not working. Now that Alkalinity and PH are good, it’s time to address Chlorine.

Shock Chlorine- Breakpoint chlorination is the point where the demand for chlorine has been fully satisfied in terms of chlorine added to water. This won’t take long to show up mixed with the pool contents.

When Testing Pool Water leaves the filter system on. If you maintain the pool water at around 1 ppm, you need to add enough shock to bring the result up to 10 ppm. That should be plenty of chlorine to create a breakpoint effect to shock the pool.

There is a formula that you can use based on 10x the number of chloramines in the pool. It goes like this. If you initially measure Combined Chlorine at .05 ppm you need a residual of about 5.0 ppm Free Chlorine to reach that threshold of Breakpoint Chlorination.

1. Measure Combined Chlorine before shocking 

2. Do the second test around 30 minutes after shocking the pool. (always shock your pool at night)

3. Then another test the next morning

Cyanuric Acid-The purpose of a stabilizer also known as Cyanuric Acid, CYA, or Conditioner in the water is to protect chlorine from the destructive ultraviolet(UV) rays of the sun. Without a stabilizer in the swimming pool, the UV rays of the sun can leave zero free chlorine in just a few hours.

Proper levels of stabilizer can result in Free Chlorine residuals remaining three to ten times longer in the pool water. When adding chemicals, it is recommended to add half, wait for one full turnover, re-test/calculate, and dose again as necessary. Some dry Stabilizers can take days to fully dissolve. So testing in a week or so is desirable for a good result. There is a good reason not to mix chemicals together to increase the speed of adding chemicals to your pool.

Will Mixing Pool Chemicals Make Them Work Faster


Most pool chemicals are incompatible and should never be mixed together. Mixing organic chlorinating agents and inorganic chlorinating agents (such as sodium hypochlorite) can lead to fires, explosions, and chlorine gas release.

Don’t use sodium hypochlorite in the pool water containing muriatic acid, a chemical used to lower total alkalinity that can also produce chlorine gas and harmful reactions.

Adding Shock Chlorine to water with high concentrations of metals or enzyme-based products is dangerous. Mixing Shock Chlorine together in trying to save money is a mistake and can lead to an explosion or a reaction. All chemical products use different ingredients so NEVER MIX POOL CHEMICALS TOGETHER!

Safe storage of chemicals to keep them dry and out of the weather along with separate is important for pool safety. Shock Chlorine and Algaeside– As a rule of thumb I never mix shock and algaecide. I shock the pool only at night and add Algaecide the next morning. Shock Chlorine has a negative effect on the ingredients of algaecide and makes it ineffective.

Chlorine and Bleach -In case your mom didn’t tell you never mix ammonia and bleach together. Mixing bleach and ammonia produces extremely dangerous toxic vapors.  Bleach decomposes to form hydrochloric acid which reacts with ammonia to form toxic chloramine fumes that can kill you.

Empty pools especially Inground pools being cleaned and prepped to be painted in-between seasons can become Confined Spaces. Be careful working inside an Inground Pool.  Don’t underestimate paint, chemicals, and your Inground Pool.

ACIDS AND CHLORINE/BROMINE- Don’t add acid and chlorine or bromine together! Muriatic acid and sulfuric acid (liquid acid), and chlorine together make a poison similar to mustard gas.

ALKALI AND ACID- They will neutralize each other and lose their effectiveness.

SHOCK AND ALGAECIDE– always add Shock Chlorine at night and the Algaecide the following day.

CHLORINE SHOCK AND SURFACE SKIMMER– The skimmer ports might use a chlorine tablet or stick that is made of different ingredients and that could be dangerous.

Use a basket leaf basket before you vacuum your pool and try a vacuum the walls of your pool along with the floor and steps.  A Basket type of skimmer can save on pool equipment and chemicals by using a little oomph!

But another great piece of Pool equipment that will last for years and If you go through Vacuums year after year as I do could be the best investment you can make for your Pool. Buy a good one.

Pool chemistry takes a little time to balance out to where it needs to be. One thing leads to another then you are back in the Pool store so take your time and make small changes in order.

You can always lower the Chlorine levels in your pool.

If the Chlorine residual gets too high there are a few things you can do to bring it down fast.  You can be the Master of your Pool saving money and enjoying as I did for years to come.


What Pool Chemicals Cannot Be Added At the Same Time?

Most common swimming pool chemicals are incompatible with each other & shouldn’t be mixed or stored together. Mixing organic chlorinating agents for pools & spas like (trichloroisocyanuric acid) & inorganic chlorinating agents (sodium hypochlorite) can lead to adverse reactions……………………………………………….. Read more


JimGalloway Author/Editor


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