Whiteboard Wednesday : Pool Chemistry 101

Welcome to Pool Chemistry 101! In this video Blake talks about five important chemicals that you should keep track of in your swimming pool. These are not the only chemical levels, but they are the most important ones to understand. If you don’t want to watch the video, you can see the details for each chemical below.

Free Chlorine (FC)

What is FC?

Free Chlorine is the sanitizer that is going to keep your pool safe and free of germs. When there is FC in your pool, its available to breakdown organic matter – like algae – to keep your pool safe.

Why FC is important

FC can be consumed one of two ways: by breaking down organic matter like algae, or it can burn off from the sun. For that reason, it is important to understand that you need to continuously replenish the FC level in your pool. If you let your FC level get too low, then your pool could become unsafe or suffer from an algae bloom. It is much easier to maintain proper FC levels on a daily basis, than eliminating an algae bloom after letting FC slip too low.

Ideal Level of FC

The ideal FC level in your swimming pool will vary based on your CYA level, which we will get to in a minute. If you have the recommended level of CYA (30-50), then your ideal range for FC is 2-4ppm.

How to adjust FC

Chlorine will continuously be depleted from your pool, so there is no action needed to lower FC level. If you need to raise your FC level, you can use Chlorine Tabs (also adds CYA), Di-Chlor (also adds CYA), Cal-Hypo (also adds CH), or liquid chlorine (bleach).

Acidity (pH)

What is pH?

pH is the acidity level of your pool, so it will indicate how acidic or basic your pool is.

Why pH is important

It’s important to have pH within the recommended range because if it gets too low, it will burn your eyes or skin. If pH gets too high, it can damage metal components of your swimming pool.

Ideal Level of pH

7.4 – 7.8

How to raise pH

pH tends to drift up over time, especially with high TA levels. Raise pH using pH-Increaser (or soda ash).

PH can be raised using borax, soda ash, or aeration. Borax raises pH and also raises TA level a little bit. If your TA level is low, use soda ash to raise both the PH and TA levels. If your TA level is high, aeration is best because it will not raise the TA level at all. However, aeration is a slow process compared to the other options.

Aeration can be provided by a SWG, spa jets, waterfall, fountain, return pointed up so it breaks the surface, air compressor, kids splashing, rain, etc. It can take some time for aeration to raise the PH. The higher your TA level, the faster aeration will raise pH.

How to lower pH

You can lower pH by using pH-Reducer (also known as dry acid). You can also use Muriatic acid, which is cheaper, though it can be a pain to handle. It’s best to use muriatic acid if you have a salt water generator (SWG). If you don’t have a SWG, and handling muriatic acid bothers you, you can use dry acid. Muriatic acid is available in various strengths. The most common strength is called either 20° baume or 31.45%. 10° baume or 15.725% is easier to handle but you need twice as much and it is usually more expensive.

Muriatic acid should be added to the pool by pouring slowly in front of a return jet with the pump running. You should pour slowly enough that pouring an entire jug takes more than two minutes. Leave the pump running for at least 30 minutes after adding muriatic acid.

Total Alkalinity (TA)

What is TA?

TA stands for Total Alkalinity, which will buffer the changes in your pH level.

Why FC is important

TA stands for Total Alkalinity, which will buffer the changes in your pH level. If you have low TA, your pH level is going to be wild going up and down a lot. If you have high TA, then your pH is going to drift up pretty quickly.

Ideal Level of TA

70-90+ ppm

How to raise TA

Raise TA with Alkalinity Increaser or baking soda.

How to lower TA

  • Add pH-Reducer (or acid) to lower your PH to between 7.0 and 7.2 (this also lowers TA)
  • Aerate until PH rises to around 7.6 (the only way to raise PH without also raising TA)
  • Repeat steps 1 and 2 until you reach the desired TA.

Calcium Hardness (CH)

What is CH?

CH stands for Calcium Hardness. Just like it sounds, CH measures how much calcium is in your swimming pool.

Why CH is important

If you don’t have any calcium in your water (and you have a plaster or gunite pool), then the water is going to dissolve the calcium out of the walls of the pool. If your calcium level gets too high, you can get calcium scaling (which is a pain to deal with).

Ideal Level of CH

The ideal level, assuming you have a plaster or gunite pool, is 250-350 ppm. If you have a vinyl pool, you don’t need any calcium at all, but it won’t hurt anything as long as it’s below the 350 level.

How to adjust CH

To increase your CH level, you can use Calcium-Increaser

Cyanuric Acid (CYA)

What is CYA?

CYA, or Cyanuric Acid, acts like sunscreen for the free chlorine in your pool. We talked about how FC can be consumed by breaking down organic matter, or by burning off from the sun. Well the CYA helps reduce that burn-off from the sun, but it also lowers the effectiveness of the free chlorine less to fight algae.

Why CYA is important

You definitely want some in your pool, otherwise your chlorine will evaporate from your pool quickly. But if you have too much, then the free chlorine isn’t going to be able to do it’s job and keep your pool sanitized.

Ideal Level of CYA

If you have a saltwater generator, the recommended level is between 60-80ppm.
If you don’t have a saltwater generator, then you want to be between 30-50ppm.

How to raise CYA

You can raise your CYA by adding Cyanuric Acid (often called Stabilizer). However, it is important to keep in mind that if you use chlorine tabs or granular Di-Chlor, then your CYA is going to drift up over time.

How to lower CYA

Unlike the other chemical levels on this list, the only way to lower your CYA is by replacing water, or through reverse osmosis. This is critical to keep in mind because

If you have a brand new pool, you should test your water as often as possible to get familiar with the pool. Once you are familiar with you levels and understand how they shift, you can switch to testing these levels weekly. Free chlorine should be tested every few days to avoid an algae bloom.

If you have any questions about these chemical levels, or any other chemicals in your pool, feel free to comment below.

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When Kevin’s not enjoying the water himself he’s engaging himself in the wide world of pool and spa knowledge which he passes on to our customers through producing content for our blogs and website. Outside of the pool world you can find him enjoying life with friends, family and his off the wall dog Brixton.