Testing Kits

[srw78]

Ok,

I have a 24' above ground pool and am currently using chlorine. Last night I bought a SWG (got a GREAT price) and am thinking about switching. I am now using thoose cheap testing strips, but I kno I need something better.

My question is, will the Taylor 2006 kit that you all keep raving about ork for both the chlorine and the SWG? It seems that it will work, but sometimes I need the answer Barney style, rather than having to figure it out on own.

Thank in advance for your paitence in my ignorance and you answers.

Sara

[chem geek]

Yes, the Taylor K-2006 will work fine for your SWG pool. An SWG pool IS a chlorine pool. The only difference is that the chlorine is generated on-site (from the extra salt in the water) in the SWG cell rather than you adding it manually.

[Dman1]

Another newbie question regarding these test strips, I have a quick question regarding the reading of them. The instructions state to dip the strip in the pool and quickly remove it, hold it level for 15 seconds, and compare the readings with the chart on the bottle. The problem is, after 15 seconds, the colors are still changing (in fact, at that point, they barely even changed color from the dry strips they once were). Is the 15 seconds BS, and should you let the colors change until they appear to stop changing? That's how I have always read it so far, and changed my pool chemistry based on that. Most of my numbers are good, except the PH is around 7.8 to 7.9, and I was looking to lower it, but I wanted to make sure I was reading the strips correctly. I have a SWG system, if that makes any difference.

Should I look at getting a more extensive test kit rather than stick with the strips? I am just using the strips now since they came with the pool.

[chem geek]

The strip can't even measure Calcium Hardness -- they only measure Total Hardness (which includes magnesium which doesn't matter for plaster pools; it's calcium that is important). They don't measure Total Alkalinity (TA) or Cyanuric Acid (CYA) within 10 ppm. You should invest in a good test kit. It's the best money you'll spend on your pool.

[Dman1]

The strip can't even measure Calcium Hardness -- they only measure Total Hardness (which includes magnesium which doesn't matter for plaster pools; it's calcium that is important). They don't measure Total Alkalinity (TA) or Cyanuric Acid (CYA) within 10 ppm. You should invest in a good test kit. It's the best money you'll spend on your pool.

The test strips I use are three way and measure Free Chlorine, PH, and TA (http://www.qualityinflatables.com/59635.html). I will look into a better test kit (any suggestions? I seen one at Walmart that was a liquid solution type test kit...would this work, or should I go to a pool store?). Would it be reasonable to use that type of kit, say, weekly, and use the strips on a daily basis (just to make sure the pool chemistry is not too far out of whack?

Also, back to my original question, is it reasonable to check the strips after 15 seconds, or after they stop changing color? I figure I might as well finish using the strips that came with the pool.

[chem geek]

For the test strips, I'd wait until the colors are fully developed.

The Walmart test kit that is a re-branded Arch Chemical HTH 5-way chlorine test kit isn't bad. The only issue with it is that the chlorine test uses DPD which can bleach out above 10 ppm FC. For an inexpensive test kit, it's OK. If you then wanted to add the FAS-DPD capability, you could just get that at tftestkits.net here though you might a well just get the entire TF100 if you go that route.

[coppersnowblue]

You should consider a Palintest kit. It has tablets witch have a longer shelf life and pre-measured reagent instead of counting drops. Also the pH reagent removes the chlorine from the sample which gives you a true reading.

[chem geek]

The Taylor kits also have a special blend of chlorine neutralizers in the pH test that works up to an FC of around 10 ppm or so (above that, no test kit measures pH properly, even if you use chlorine neutralizer because such neutralizers change the pH unless very carefully balanced). As for the chlorine test, you can see a demo of the FAS-DPD test here. It is accurate to within 0.2 ppm for both Free Chlorine (FC) and Combined Chlorine (CC). The drop-based tests for Total Alkalinity (TA) and Calcium Hardness (CH) are within 10 ppm (though with CH you usually use a sample size to measure within 25 ppm). The Cyanuric Acid (CYA) test is a turbidity test that has a precision of 10 ppm, but is the hardest to see as shown here.

Though Taylor says their reagents should generally be replaced every year, in practice most last at least 2 years. The FAS-DPD titrating reagent is the most sensitive, but is also the one you use up most quickly.

[Dman1]

Thanks guys. This info is greatly appreciated.

[coppersnowblue]

The Taylor kits also have a special blend of chlorine neutralizers in the pH test that works up to an FC of around 10 ppm or so (above that, no test kit measures pH properly, even if you use chlorine neutralizer because such neutralizers change the pH unless very carefully balanced). As for the chlorine test, you can see a demo of the FAS-DPD test here. It is accurate to within 0.2 ppm for both Free Chlorine (FC) and Combined Chlorine (CC). The drop-based tests for Total Alkalinity (TA) and Calcium Hardness (CH) are within 10 ppm (though with CH you usually use a sample size to measure within 25 ppm). The Cyanuric Acid (CYA) test is a turbidity test that has a precision of 10 ppm, but is the hardest to see as shown here.

Though Taylor says their reagents should generally be replaced every year, in practice most last at least 2 years. The FAS-DPD titrating reagent is the most sensitive, but is also the one you use up most quickly.

I would like to see the info on the Taylor phenol red with the special blend. Will you tell me where I can find it? It would help me greatly. thanks

[chem geek]

They told me this over the phone when I contacted them a while ago (after some E-mail exchange). I had noticed that some pH tests from other manufacturers have you add sodium thiosulfate (chlorine neutralizer) to the sample before doing the pH test so I asked them why they don't do that in their instructions. They said that sodium thiosulfate can change the pH in somewhat inconsistent ways and that they use a proprietary blend of chlorine neutralizers designed to not affect the pH. I had done some tests myself with sodium thiosulfate and chlorine and did find it to affect the pH which is why I initially called.

Nevertheless, the pH test will still be affected negatively above around 10 ppm FC (the precise level depends on TA and other factors) and Taylor talks about this in the booklet (though it seems to imply an effect above around 5 ppm, but tests I made with standard samples and fixed amounts of chlorine and pH balancing seemed to handle 10 ppm FC with no problem).

As with anything else, the best approach is to do tests yourself. I know what the theoretical pH should be from various chemical additions by using a spreadsheet I wrote here. You can add chlorine to buffered (say, pool) water samples and add some acid as needed to adjust pH and then measure to see if the results come out as predicted.

The following is from Taylor's Pool & Spa Water Chemistry booklet:

FALSE READINGS: high levels of chlorine (usually > 10 ppm) will quickly and completely convert phenol red into another pH indicator (chlorphenol red). This new indicator is a dark purple when the water's pH is above 6.6. Unfortunately, some pool operators mistake the purpole color for dark red and think the pool water is very alkaline and wrongly add acid to the pool.

When a sanitizer level is not extreme, only some of the phenol red may convert to chlorphenol red. However, purple + orange (for example, pH 7.4) = red. This error is more subtle as no purple color is observed and the operator does not suspect that a false high pH reading has been produced. Some operators neutralize the sanitizer first by adding a drop of chlorine neutralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.

When I did some tests, I wanted to see what very high chlorine levels would do. I found that though initially it created a purple color, it then reverted back to a normal pH indicator color as if the chlorine were neutralized. This was technically too low since the pH was legitimately higher with the chlorine (though should not look like the purple of chlorphenol red if there were no interference), but it did show that some sort of chlorine neutralizer is indeed in the pH indicator dye solution. At lower FC, the pH seemed to be as predicted. If you do your own experiments, I'd be interested in the results.

Richard

[coppersnowblue]

They told me this over the phone when I contacted them a while ago (after some E-mail exchange). I had noticed that some pH tests from other manufacturers have you add sodium thiosulfate (chlorine neutralizer) to the sample before doing the pH test so I asked them why they don't do that in their instructions. They said that sodium thiosulfate can change the pH in somewhat inconsistent ways and that they use a proprietary blend of chlorine neutralizers designed to not affect the pH. I had done some tests myself with sodium thiosulfate and chlorine and did find it to affect the pH which is why I initially called.

Nevertheless, the pH test will still be affected negatively above around 10 ppm FC (the precise level depends on TA and other factors) and Taylor talks about this in the booklet (though it seems to imply an effect above around 5 ppm, but tests I made with standard samples and fixed amounts of chlorine and pH balancing seemed to handle 10 ppm FC with no problem).

As with anything else, the best approach is to do tests yourself. I know what the theoretical pH should be from various chemical additions by using a spreadsheet I wrote here. You can add chlorine to buffered (say, pool) water samples and add some acid as needed to adjust pH and then measure to see if the results come out as predicted.

The following is from Taylor's Pool & Spa Water Chemistry booklet:

FALSE READINGS: high levels of chlorine (usually > 10 ppm) will quickly and completely convert phenol red into another pH indicator (chlorphenol red). This new indicator is a dark purple when the water's pH is above 6.6. Unfortunately, some pool operators mistake the purpole color for dark red and think the pool water is very alkaline and wrongly add acid to the pool.

When a sanitizer level is not extreme, only some of the phenol red may convert to chlorphenol red. However, purple + orange (for example, pH 7.4) = red. This error is more subtle as no purple color is observed and the operator does not suspect that a false high pH reading has been produced. Some operators neutralize the sanitizer first by adding a drop of chlorine neutralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.

When I did some tests, I wanted to see what very high chlorine levels would do. I found that though initially it created a purple color, it then reverted back to a normal pH indicator color as if the chlorine were neutralized. This was technically too low since the pH was legitimately higher with the chlorine (though should not look like the purple of chlorphenol red if there were no interference), but it did show that some sort of chlorine neutralizer is indeed in the pH indicator dye solution. At lower FC, the pH seemed to be as predicted. If you do your own experiments, I'd be interested in the results.

Richar

Thanks for the info. I have experimented some but not very scientific and didn't take enough notes but plan to do more this summer. I have had the same luck with Palintest the tech support guy told me they add a chlorine neutralizer but Taylor and Lamotte do not. When I do a comparison the Taylor always seems to read lower but I am using a Palintest photometer when I compare to a Lamotte photometer it seems to read low like the Taylor comparator. These comparisons have been at fcl levels of 3ppm or less.

[chem geek]

Thanks for the info. I have experimented some but not very scientific and didn't take enough notes but plan to do more this summer. I have had the same luck with Palintest the tech support guy told me they add a chlorine neutralizer but Taylor and Lamotte do not. When I do a comparison the Taylor always seems to read lower but I am using a Palintest photometer when I compare to a Lamotte photometer it seems to read low like the Taylor comparator. These comparisons have been at fcl levels of 3ppm or less.

The DPD test isn't going to be very accurate if using a comparator. Even using a photometer it will only be accurate if calibrated properly and accounting for the bleaching effect of chlorine on the DPD dye itself. You cannot reliably measure higher than 5 ppm FC since the chlorine will bleach out DPD and above 10 ppm FC it may be completely bleached out. A more accurate way to test is to use the FAS-DPD chlorine test as shown here. It is accurate to within 0.2 ppm FC (when using a 25 ml sample size; has a resolution of 0.5 ppm when using a 10 ml sample size). It measures Combined Chlorine (CC) separately, also to within 0.2 ppm CC, and it doesn't bleach out so can measure even high shock levels up to 50 ppm (you just add more DPD powder if you see a flash of pink). It is because of this chlorine test that is why I recommend the Taylor K-2006 or the TF100 from tftestkits.net.