I Just Filled My Pool With Water - Now What?

I Just Filled My Pool With Water - Now What Do I Do?

Opening a pool can be a complex process. You may find yourself wondering: I just filled my pool with water, now what? There are many factors of your pool’s water that need to be balanced before the pool is ready for swimming, but it can be difficult to know where to start.

In this article we will lay out the steps for how to prepare your newly filled pool for swimming, including how to test and balance your pool's chemistry, treat your water, and add maintenance products.

Run Your Filter

If you have just filled your pool with water, the first thing you should do is turn your pump on and allow the filter to begin cleaning and circulating your water.

Stagnant water that is untreated can quickly develop bacteria, so it is a good idea to keep the water flowing as you prepare for the next steps.

Ideally, you should run your filter for a 24 hour period after filling your pool. During this time period, you can continue to prepare other factors of your pool water’s chemistry for swimming.

Test And Balance Pool Chemistry

The second thing you should do after filling your pool with water is test your pool’s chemistry. We recommend using a test kit that tests for multiple levels, such as the Aquachek 7 Test Strips.

These test strips test for seven chemical properties: cyanuric acid, free chlorine, combined chlorine, pH, bromine, total alkalinity, and calcium hardness.

While all of these properties are important, the most essential ones to focus on when first opening a pool are the pH, total alkalinity, and calcium hardness. We recommend getting a test kit with these components, in addition to a test for free chlorine.

Adjusting Total Alkalinity

The first chemical property you should test and adjust in your pool is the total alkalinity. Total alkalinity acts as a buffer for your pH levels, preventing them from undergoing rapid changes.

Because adjusting your total alkalinity can affect your pH levels, we recommend you do this step before measuring and adjusting pH.

Ideal levels for total alkalinity in a pool range from 80-120 parts per million (ppm), with the sweet spot being at 100ppm.

If your pool has low levels of total alkalinity, use baking soda, also known as sodium bicarbonate, to raise it. To figure out how much baking soda you need to add to your pool, you can use our baking soda calculator.

Although unlikely, if your total alkalinity levels are too high upon filling the pool, you will need to lower them.

To do this, you can use sodium bisulphate or hydrochloric acid. To figure out how much you should add to your pool, you can use our pool alkalinity calculator.

Regulating pH Levels

After adjusting your total alkalinity and allowing the water to circulate for a couple of hours, test your pH levels to see if they need further regulation. Because correcting total alkalinity changes pH levels, your pool may need more or less adjustment than it did previously.

Ideal pH levels for a pool range from 7.2-7.6. If your pH levels are high, you can use hydrochloric acid or sodium bisulphate to lower them. The alkalinity calculator we mentioned earlier can come in handy here.

If your pool’s pH levels are low, you will need to increase them using soda ash. Soda ash will lift the pH substantially without having as great an impact on your total alkalinity as baking soda.

Ideal Calcium Hardness

Ideal calcium hardness levels in a swimming pool range from 200-400ppm. If your calcium levels are too low, you should use a hardness increaser to raise them. Water with low calcium hardness develops corrosive properties, which can cause damage to your new pool.

This phenomenon is most clearly seen in plaster and concrete pools, which end up with ‘plaster dust’ if the calcium hardness is not balanced properly while you are filling.

Plaster dust may sound harmless, but it is actually a sign that your new pool surface has already started degrading.

Don’t forget to adjust your calcium hardness as you fill your pool!

Use Water Treatments

After balancing these properties of your pool’s chemistry, you will then want to introduce a couple of treatment products to your water. When opening a pool, it is recommended that you use a clarifier and a shock treatment.

Shocking Your Pool

It’s important that you shock your pool early to create and maintain a free chlorine level.

This is important because it rapidly kills off any microorganisms like bacteria and algae that may have been present in your fill water and prevents them from establishing themselves in your pool.

By maintaining a free chlorine level, you ensure that your pool remains a sanitary and safe environment for swimmers. Find out how much chlorine to add by using our calculator.

I recommend using either calcium hypochlorite (granular) or sodium hypochlorite (liquid) chlorine as these are both unstabilised (ie. don’t contain cyanuric acid), as we will add stabiliser separately later.

Read more about the difference between liquid and granular chlorine.

Using A Clarifier

Clarifiers are another treatment that is often recommended for opening newly filled pools. The products work by causing tiny particles of debris in your pool’s water to stick together, allowing them to be trapped by your filter system more easily.

This step is great for removing any pre-existing debris in the source water that may be too small for your filter to catch under normal circumstances. If your source water is cloudy or murky, clarifiers are an essential step.

Introduce Maintenance Products

After you have performed the above steps, you will need to introduce your pool’s primary maintenance products. This should include a stabiliser when setting up an outdoor chlorine or salt pool, and also an algaecide.

Adding Stabiliser

Stabiliser is a pool chemical which contains cyanuric acid, an essential component of pool water chemistry. It increases the longevity of your chlorine by protecting the molecules from being degraded by the UV in sunlight.

Without sufficient levels of cyanuric acid (30 - 50 ppm), your chlorine can disappear in a matter of hours on a sunny day!

Use this calculator to find out how much stabiliser to add to your pool.

Using Algaecide Preventatively

Algaecide is commonly used when treating algae problems, but did you know it is actually intended to be used as a preventative product? Algaecides can be added to your pool upon opening in order to continuously eliminate algae problems before they become noticeable.

We recommend using an algaecide when opening your pool because one dose can prevent algae growth in your pool for up to three months.


Opening a newly filled pool can be a lengthy process. Because many factors of your water quality need to be adjusted, it can be difficult to know what order you should follow when balancing your pool’s chemistry.

Luckily, we have created an easy list of steps (and a checklist of chemicals) you can follow to get your pool up and running in no time.

Do you have any questions about how to open your newly filled pool? Get in touch with us in the comments, we’d love to help!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.