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Water Chemistry

Water Chemistry / Testing


The Pool Forum website that Ben Powell created has been invaluable in getting me up to speed on a lot of the technical details of how to maintain water chemistry in a pool.  Reading through many of the postings in the Testing and Adjusting Pool Water Chemistry forum, I discovered a few things that seemed to be a general consensus among the members:

CONTINUED BELOW

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  1. Most of the information from pool stores and specifically their computerized water testing services are of the devil.

  2. Ben Powell's test kits are the best on the market and worth their weight in gold.

  3. Ben Powell's test methods will result in a sparkling clear pool if administered properly.

I have no idea if any of these statements are true, but one thing seemed pretty clear: people seemed to be pretty happy with the results of their pool once they started to use Ben's test kits and testing methods.  In fact, after hours scouring various forums up on the Pool Forum, its a rare posting that speaks about Ben's test kits and testing methods in a negative way.

The one test kit in particular that seemed to be the end-all as far as test kits go was the PS-233.  It was $67 + $7 for shipping.  I decided to follow along with the crowd and I ordered mine just before Christmas.

This page will chronicle my attempts at getting the water in my pool chemically balanced.  I'm starting at the newbie level, so you'll have to bear with me as I start this new chapter in my pool ownership experience.

Friday, January 18, 2003
The PS233 test kit finally arrived today.  I couldn't wait to tear it open to see what was inside.  I quickly tore open the box and found inside a very sharp-looking and neatly arranged translucent plastic case with a dozen or so small compartments.  It was very impressive.  The compartments held various aqueous solutions in little drop bottles and it even came with a little pencil and eraser to record test results on the top of the plastic case.

       

Since the pool is not completed at the time of this writing (still have the pebble interior to go), I decided I would test the tap water first, since it will be the source of the initial fill water.  I will be plumbing the auto-water leveler to a soft water source, so I will also be testing that as well.

Saturday, January 19, 2003
One difficulty I encountered was trying to find information about the main measurements (TC, CC, FC, PH, TA, CH, and CYA) that people mention when posting their results to the pool forum.  There was one page on the Pool Solutions website that seemed to have the information I was looking for - the "Test Kit Basic Terms" page, but part of the problem was that it never used any of the popular acronyms.  It took me awhile to figure out what they stood for and how they mapped to the terms used on that page.  Another difficulty was that the page seemed to mix a lot of different types of information together (bolded terms are the main subject headings on the page):

  • Major Test Measurements - pH, Alkalinity (TA), Calcium Hardness (CH), and Stabilizer (CYA)

  • Indicators - DPD and OTO that are used to measure Chlorine (TC, FC, and CC) with various degrees of accuracy.

  • Test Methods - Drop Count (titration), which explains how to administer the tests.

  • Less Useful Test Measurements - Acid Demand.  According to Ben, its less useful for homeowners since we have the luxury of frequent testing.

  • General Terms - Acid and Balanced Water

Since a majority of folks seemed to key their testing off the PS232 / PS233 test kits, I think it would have been easier to make the connection if it were based on the main measurements (along with the popular acronyms) and to put all the supporting information under those instead.  Still, the Test Kit General Overview page at the Pool Solutions site was very informative and is highly recommended.

Once I finally put it all together in my head, I started my testing.  Here are the individual tests that I ran and the results.

Free Chlorine (FC)
Also known as Available Chlorine, this is the amount of chlorine in your pool water that is available as a sanitizer.  For concrete pools like mine, Ben says that the amount has to be above 0.5ppm and must go above 5.0 (shocking) per week.  If the FC value is too low, and the pool would be unsafe to swim in.  If FC is too high, it could lead to discoloration for vinyl pools, irritated skin, eyes, and green hair.  The optimum amount of chlorine you should have depends on your Stabilizer (CYA) levels.  The higher the CYA levels, the higher the FC needs to be.  The testing for FC is achieved through a titration test where you count the number of drops of a FAS-DPD reagent added to a 25ml sample of pool water that's been dyed pink with DPD powder until the pink color disappears.

                       

Combined Chlorine (CC)
This is chlorine that is combined with contaminants and is useless as a sanitizer.  Ideally, you should have no CC in your pool water.  Having a CC value over zero means there is presence of  irritating chloramines (stuff that gives off that chlorine smell) in your pool.  Getting rid of CC is done through shocking.  The test for the presence of CC is done through another titration test (using the same reagents pictured above) where a drop count of another reagent is used to see when a color change occurs.

Total Chlorine (TC)
This is the total chlorine that is in your pool and is typically FC + CC, but there is a colormetric test used to determine a rough ballpark value for TC.  The PS-233 test kit comes with a PS-200 sub test kit that comes with a combined OTO/Phenol Red tester for TC and PH.  The side that contains the yellow OTO solution tests for TC.

        

pH
This is the measurement that tests the acidity of the pool water.  A value of 7.0 is considered neutral.  Anything above 7.0 is considered basic and below 7.0 is acidic.  The optimum range for pool water should be between 7.4 and 7.8, which is slightly basic.  If the water is too acidic, I'm told it could corrode plaster or vinyl pool surfaces.  If its too basic, calcium in the water combines with carbonates in the water to produce calcium carbonate or scale. Also, calcium carbonate can form into tiny particles and float around in the water giving the water a cloudy, turbid appearance.  The PS-200 test kit contains a Phenol Red test kit for a colormetric PH test.

                       

Total Alkalinity (TA or "Alk")
This acts as a pH buffer and stabilizer to prevent pH from swinging wildly.  Having too low a value of TA can cause corrosion of the surface of a concrete pool (plaster or pebble-tec).  Having too high a value of TA leads to excessive scaling at the waterline and heater elements.  TA is measured using another titration test in which drops of a sulfuric acid solution into a chemically green-dyed water sample are counted until the sample turns red.

       

Calcium Hardness (CH or CA)
Measures the amount of dissolved calcium is in the water.  Too little CH (< 100ppm), and calcium will get leached from the pool's surface causing damage through erosion.  Too much CH (>250ppm is considered Hard Water), and scaling will be an issue at the waterline and heater.  BTW, Arizona is notorious to hard water and this is something that I plan on monitoring carefully.  I will be hooking up a soft water source to the auto-water leveler as a way to keep the CH value down.  CH is measured using another titration test in which drops of a hardness reagent into a chemically red-dyed water sample are counted until the solution turns blue.

        

Cyanuric Acid or "Stabilizer" (CYA)
By combining with chlorine, stabilizer protects chlorine from being destroyed by the UV rays in sunlight.  It does so effectively by putting it in reserve.  Without CYA or too little of it, the chlorine in the top 12 inches of your pool can get destroyed in as little as 15 minutes.  Too high of a CYA value, and it reduces the ability of chlorine to sanitize, increasing the potential of having algae problems and requiring higher levels chlorine to operate your pool.  Generally, most folks seem to think that levels of stabilizer from 30 ppm to 70 ppm are about right.  The CYA levels in the pool are measured using a turbidimetric test where a solution of pool water and a CYA reagent are vigorously mixed together and allowed to settle before being slowly poured into another vial with a black dot on the bottom.  The stabilizer is measured by the amount of solution poured into the vial required to make the black dot disappear.

       

Results?
Like I mentioned earlier, since I'm still waiting for the pool interior to be done, I thought I'd start off my measuring the fill water which will be supplied by the City of Chandler tap water supply and also the water that will be used to top-off the pool.  This water will come from a soft water source through the auto-water leveler (AWL).  Here are the results from the testing:

                   

It looks like the Total Alkalinity (TA) and Calcium Hardness (CA) for the raw tap water is in line with what I've been told Arizona water is - very, very hard.  In contrast, the soft water has a CA value of only 20 ppm, while the TA is down only slightly.  It looks like I'll have to lower the pH of the pool and aerate the heck out of it until the TA comes down to a more reasonable level.  Both the soft and hard water sources have no Stabilizer (CYA) which is expected.   The pH is near where I want it to be, but it will change due to getting some of the other measurements (TA, and FC) to where they need to be.

For me I think the biggest challenge will be to keep the CA and TA levels low enough to:

  1. Keep the scaling problems around the waterline down to a minimum.

  2. Prevent damage to the heater elements and the salt water chlorinator's salt cell / electrode.

I think the rest of it will a lot easier to deal with than the hard water issue.  That's about all I can test for now until the pool's interior gets done.  Sometime between now and filling the pool, I also need to hook up the soft water source to the AWL.  The work should involve installing a couple of valves and PVC connectors so it shouldn't be too difficult.

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