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 water problem or your 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, pumping rate of the filter system & how much chemical needed. 
Alkalinity takes 6 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 pool.


How Long do You Wait Before Adding Different Chemicals to Your Pool

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 is the key to how long you filter your pool to recirculate and turn it over. To get 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.

Turnover rate- 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 some chemicals along mixing the pool by hand using a skimmer that will help make it faster. For Alkalinity Adjustments, I would wait the turn-over 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 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 then the other. Stabilizing Alkalinity to hold off using PH adjustment for 2 to depending how big your pool is 4 hours. The chemistry involved in Alkalinity is the base for other required chemistry to work off of.

PH and Disinfection (chlorine) are dependent on the Alkalinity to be rock solid inside that 80-120 ppm for everything to click and this where I recommend some time.  Total Alkalinity is a buffer or sponge that resists rapid pH change is 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 allowing algae, bacteria, and other contaminants to grow. It can also cause clogged filters, clogged heater elements, and reduced circulation as a result of 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 towards the bottom-center of the pool and creates 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 Should You Wait To Test Pool H2O after adding Chemicals

Once a chemical establishes itself and its where its need 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 then stop, it may even stop sooner than later or it may take a little longer.then move on.

PH- Then you can add the PH adjustment. With PH Plus and PH minus or with Muriatic Acid that 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 wait for re-testing PH. Some Pool Suppliers recommend a full cycle turn-over which in this situation would be 6 hours but you’ll be able to see if it is still moving or fluctuating.

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

I would also suggest using reagents when doing pool testing but that’s up to you. Test strips go bad and are not reliable. Buy a reliable test kit and spend a few dollars more if you can.

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. Leave 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 is based on 10x the amount of chloramines in the pool. It goes like this. If you initially measure Combined Chlorine at .05 ppm you need a residual of about 5.0ppm 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 at night)

3. Then a another test the next morning

Cyanuric Acid-The purpose of 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 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 Stabilizer 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.

Mixing Pool Chemicals Won’t Make Them Work Any 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 can also produce chlorine gas and harmful reactions.

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

Safe storage of chemicals to keep them dry and out of the weather along with separated is important 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 Algaeside 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 pool being cleaned and prepped to be painted in-between seasons can become a Confined Space. I wrote an article recently about the reality of the Confined Spaces that are unnoticed on people’s properties the biggest being an Inground Pool. Be careful working inside an Inground Pool. 

I’ve seen a lot of things in my life working in Water/Wastewater and this is sadly a real occurrence.  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 The skimmer ports might use a chlorine tablet or stick that is made of different ingredients and that could be dangerous.

Use a Skimmer 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 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! 

Its found right here through MyWaterEarth&Sky on Amazon is called a Dolphin Nautilus CC Plus Automatic Robotic Pool Cleaner with Easy To Clean Large Top Load Filter Cartridges and Tangle-Free Swivel Cord, Ideal for In-Ground Swimming Pools Up To 50 Feet

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

Be the Master of your Pool. Read my earlier article that can enhance the look and feel of your Pool’s water here on  MyWaterEarth&Sky called How to Make the water in your Swimming Pool Soft, Silky Smooth.


Jim has worked in the Water/Wastewater and Water Filtration Business for over 30 years as a Consulting-Operator and has written over 250 articles on the World-Wide Water Situation.


Author/Editor, MyWaterEarth&Sky

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