Water Chemistry In Chlorine Swimming Pools

Water Is Actually A Solvent


Swimming pool water chemistry, as most pool owners know, can be a confusing topic when you look at it scientifically. Water is actually a solvent and when your pool water chemistry is out of balance it can and will try to satisfy it’s own need for certain minerals by dissolving metals it comes into contact with.

free chlorine vs total chlorineDon’t worry, there’s good news…when your swimming pool water chemistry stays in balance, the “needs” of your pool water are always met, and you can enjoy the benefits of your pool for years and years. Just remember that water is a solvent, and it can corrode, stain, dissolve, calcify and basically ruin metals it comes into contact with. That includes your pool pump, heater and other internal workings of your pool equipment.

Since water chemistry is pretty volatile and will change dramatically depending on a lot of influences, the idea is to learn about each of the chemicals that can be added to pool water to keep it in balance; then monitor your swimming pool water chemistry closely enough to keep everything in balance.

Simple, right? Actually, it doesn’t have to be too complex and it really can be fairly simple; Use the services of your local pool supply store and bring them a sample about once per month, and you can use test strips in between trips to the pool store. If you talk to them and apply what you learn from each trip, you can become knowledgeable quickly.

I am into my third season as a pool owner, and while my intentions are to be as knowledgeable as I can possibly be about pools and pool water chemistry so I can share the knowledge while I learn new things, the basics of water chemistry remain constant. There are plenty of nuances, and I learn something new pretty regularly.

Saturation Of Chemicals In Pool Water

You will see on test strips a “ppm” for nearly every element of balanced water chemistry except for PH, (which is measured on a scale from 1 to 14, where 7.0 is neither acidic nor alkaline…(being neutral on the scale). More about that later. For now, here is a rundown of the chemicals that you’ll find in a chlorine pool and what the “ideal” ranges are for different chemicals.

(You will find differences in the definition of balanced pool water chemistry from one pool professional to the next, but no one can argue that the following are all ideal ranges.)

Ideal Range Of Specific Pool Chemicals

Chlorine – minimum 1.0ppm – Ideal 2.0 – 3.0 ppm – maximum 3.5 ppm
Cyanuric Acid – Minimum 25 ppm – Ideal 30-70 ppm – Maximum 80 ppm
Bromine – minimum 2.0 ppm – Ideal 2.5-4.0 – Maximum 5.0 ppm
Alkalinity – Minimum 70 ppm – Ideal 80-140 ppm – Maximum 150 ppm
Hardness – Minimum 150 ppm – Ideal 200-450 ppm – Maximum 500 ppm

PH is measured by the pH scale as discussed earlier. The minimum pH for a chlorine pool is 7.2 (slightly alkaline). The ideal pH range is 7.4 to 7.6 and a high pH is 7.8 or higher.

Free Chlorine Versus Total Chlorine

Swimming pool chlorine has two factors; Total chlorine and free chlorine. Total chlorine is the sum of chlorine that is being utilized to kill bacteria, plus the chlorine that is unused or “free” and ready to be utilized. Free chlorine is simply the chlorine in the water that isn’t being used to kill bacteria.

The Problem With Cyanuric Acid

Most imbalances can be addressed and counterbalanced with pool chemicals. Excessive cyanuric acid cannot. Cyanuric acid is added to chlorine (and tablets) so that chlorine does not dissipate too quickly. Once cyanuric acid levels in your pool become too high, you need to drain some of your pool water out and replace it with fresh water to lower its level.

Pool Water Chemistry Test Strips

Better test strips have all the above readings on them and with practice you can get really really close to ideally balanced water using them. It is a very good idea to let your pool store test your water as well so you can “check” yourself. In case I haven’t mentioned it yet, it’s a free service as long as you don’t abuse it and you should buy a few things from them every so often. Then there are more expensive test kits that can get you on target but I like the idea of saving money and letting the pool store keep my pool chemistry zeroed in all the way.

I use the Aquachek 7-Way Pool & Spa Test Strips:

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