Pool Water Chemistry and Testing

This whole pool thing is new to me and it’s time to organize my thoughts on what/how/when things need to be done.

The BBB (Bleach, Borax, Baking Soda) method looks like the most straight forward method for maintenance. In a nutshell, do the following:

  1. Know your stabilizer concentration:
    • You have to know how much stabilizer (CYA, Cyanuric Acid) is in the water.  The more stabilizer, the more free chlorine that is required to make the chlorine effective.  For outdoor pools exposed to the sun, it’s recommended to have roughly 40-80 PPM of stabilizer to prevent the sunlight from destroying the chlorine.  Too much stabilizer (CYA, Cyanuric Acid) leads to high levels of chlorine and unnecessary bleaching of swimsuits and hair.  It seems to be a trade off of how often you want to test/add chlorine vs bleaching (less stabilizer, less bleaching, more frequent testing/maintenance).  Sensitive skin may also have issues with higher chlorine level
    • Stabilizer (CYA, Cyanuric Acid) can be measured at your pool store, or with a test kit.
    • CYA levels do not change except when you add more or remove water.  NOTE: Tri-Chlor tablets and Di-Chlor granules both  contain stabilizer — see the Chlorine Choice below!
    • Replacing water is the only way to lower stabilizer levels, so, add it carefully.
    • Once the level is established, recheck a few times a year, or after some causal event.
  2. Adjust your Free Chlorine: With stabilizer (CYA, cyanuric acid) concentration known adjust your Free Chlorine using this chart, or this chart, to know how much Chlorine  you need to maintain.
    • Add chlorine of choice to raise the level with the pump going and re-check in a few hours for granules and liquid types.
    • Use slow dissolving tablets (careful: they usually contain stabilizer!) for maintenance.
    • Re-check daily, or couple of days once established in a routine.
  3. Adjust your PH: it should be 7.2 -7.8.   The daring can run it up to 8.2 with care, if your pool naturally balances at that high range (and your test kit accurately measures that high).
    • Use Muriatic Acid to lower the PH.  Can be purchased at a hardware store.
    • Use Borax to raise the PH.  Yes, the 20 Mule borax in the laundry isle of your grocery store.
    • Use this pool calculator to figure how much.
    • Recheck weekly.
  4. Maintain the Total Alkalinity in the 60-90+ PPM range.
    • Total Alkalinity controls how difficult it is for the PH to be changed.
    • Raise it very carefully with baking soda.
    • Lowering is much harder.
    • Re-check monthly.
  5. For plaster/concrete pools, maintain Calcium Hardness above 250 PPM to avoid having calcium leach out of the plaster/concrete.
    • Add Calcium Chloride to raise it.
    • There is no maximum, but, too much will eventually lead to scaling around the water line and in the heater core.
    • Re-check monthly.

The rest of the chemistry is fairly much a non-issue.

Chlorine Choice:

Let’s assume we want to take a 20K gallons pool and raise the free chlorine by  5 PPM. What will it cost using the various products?

  • Household bleach
    • Made of Sodium Hypochlorite.  It ranges in concentration, but, let’s assume we are using 6%.
    • It’ll take 208oz (volume) to do the job.  It’ll also raise the salt in the pol by ~8 ppm.
    • At Walmart a 96 oz bottle costs $1.98, thus it would cost $4.32 for this product.
  • Granular, “Cal-Hypo”, or “Cal Chlor”
    • Made of Calcium Hypochlorite, usually 65%.
    • It’ll take 20 oz (weight) to do the job. It’ll also raise the salt by ~5 ppm, and the calcium hardness by 3.4 ppm.  This is of concern if you already have high calcium.
    • Buying a 50# bucket from my local pool supply goes for $120, thus costing $3.00 for this product.
  • Granular, “Di-Chlor”
  • Tablets or Sticks, “Tri-chlor”
    • Made of Trichlor-S-Triazinetrione, which has 90% stabilized chlorine.
    • Usually a slow dissolving tablet that’s meant to go in floating feeder or in the skimmer.
    • It’ll take 14.6 oz (weight) to do the job. It’ll also raise the salt by ~4 ppm, raise the CYA by 3 ppm, and lower the PH about 0.27 (depending on total alkalinity).
    • A 50# bucket from “in the swim” currently goes for $130, thus, costing $2.37 for this product.

So, it appears as of this writing, the most economical way to chlorinate is Tri-chlor tablets if you actually *need* to raise your stabilizer concentration, or Calcium Hypochlorite granules you have headroom in your calcium levels, and then bleach.

Dealing with Combined Chlorine (chloramines)

  • Free chlorine has no odor and does not irritate the skin in normal maintenance dosages.  Combined Chlorine (chloramines), however, does have an odor and causes irritation.  It is the source of that “over chlorinated” complaint people make.  Combined Chlorine is much less effective at sanitizing.  Chloramines will naturally dissipate through UV breakdown, but, it can be accelerated by raising the free-chlorine levels.  Use any of the fast dissolving chlorine choices above to do this — don’t pay more for special “pool shock” chlorine.
  • Reducing chloraimes (combined chlorine — CC) requires raising the concentration of free chlorine.  There’s a good article on it here that explains what’s happening.
  • Update: Here’s a better guide to shocking the pool.
  • There are also non-chlorine oxidizers that accomplish the same goal, but there’s no good reason to use them over your regular fast dissolving chlorine.
  • Shocking the pool is only needed when you have measurable combined chlorine or some other visible problem with the water.  There should be no need to do so as part of a regularly scheduled program.

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