Test Strips

[rubiconruby]

I use test strips to read the PH level in the tub and sometimes it seems like they are not reading correctly. Last week I was having trouble getting the water clear. The dealer tested my water and said it had high PH. Before treating it I tested the water with stips from 2 different bottles and it read ok. I also had someone else look to be sure I wasnt going colorblind. I added what the dealer said to and the water went clear. So my question is.....is there a better way to test the water?

[IL Parrothead]

I use test strips most of the time, but I also have a Taylor Test kit for those times where I have doubts about the strips.

[Renee]

I have the Aquacheck Tru Test Digital Tester.  I compared it to the dealer's tests several times before relying on it.   It gives you the "number" vs. the color, so you have a better idea how far you're off, instead of "guessing" by the color.  

[Water Boy]

I use test strips to read the PH level in the tub and sometimes it seems like they are not reading correctly. Last week I was having trouble getting the water clear. The dealer tested my water and said it had high PH. Before treating it I tested the water with stips from 2 different bottles and it read ok. I also had someone else look to be sure I wasnt going colorblind. I added what the dealer said to and the water went clear. So my question is.....is there a better way to test the water?

You might check a couple of things. Test strips do have expiration dates on them. If they are expired, sometimes they can be way off. One time I had a old timer that was using test strips to check his water and he swore it was reading fine, and his strips had been expired for two years. Needless to say he water was WAY off. Also, sometimes if you get any moisture in the bottle, that can throw them off as well. I would suggest getting a new bottle of test strips and recheck it.

[wmccall]

Another thing to check is the instructions for the strip. Some tell you to read immediately, or wait a few seconds. If you dip it in the water and then take a few seconds to walk to someplace with more light, the strips can continue to get darker over a short period.

[kokanee001]

My test strips test for free chlorine, total chlorine, alkalinity, pH and hardness. What is total chlorine? I just tested and noticed that it (total chlorine) was high. How do I lower it to within proper limits? I'm still a newbie at some of this water testing stuff.

[rubiconruby]

Thanks for all the info, maybe I wil get a Taylor kit. I was worried that my strips had somethign wrong with them so I tried a new bottle and still the same. I also double check the directions to be sure I had them right. Its wierd because I have been using them for years then all of a suddon I have been havign trouble. Maybe the cold air messes them up. I also like the idea of the digital one. Any idea how much it was?

[Flyonthewall]

My test strips test for free chlorine, total chlorine, alkalinity, pH and hardness. What is total chlorine? I just tested and noticed that it (total chlorine) was high. How do I lower it to within proper limits? I'm still a newbie at some of this water testing stuff.

if your total chlorine is significantly higher than free chlorine you have chloramines in the water (chlorine combined with swimmer waste such as ammonias).  using a non chlorine shock is the most effective way to treat, and avoid, this situation.

[Micah]

I don't mean to disagree with some of the experts here, but I think recommending Taylor test kits are a mistake.  Taylor makes a good kit for testing "Free Ch." and "Total Alkalinity".  However the P.H. test in a Taylor kit is the least accurate of any kit I have used.  Most good test kits use a "Chlorine Neutralizer" before adding the "Phenol Red".  Taylor is the only high end kit that doesn't.  This means that your P.H. will often show as being to high, when in fact it is not.  The P.H. test in a "Taylor" kit is no more accurate than a cheap $5.00 test kit.  

When looking for a test kit I would recommend looking for the following:
Make sure it has at least 4 solutions.  Stay away from "2 in 1 kits".
Make sure it has a "Chlorine Neutralizer" for both the P.H and Total Alkalinity.
Make sure it tests for "Free Chlorine" as well as Total Chlorine.  (look for D.P.D. not O.T.O.)

[chem geek]

The pH indicator solution in the Taylor test kit already has some amount of chlorine neutralizer in it which is why you do not need to add any and the pH is accurate until the sanitizer level gets high, especially above 10 ppm.  The reaction of chlorine neutralizer with chlorine changes the pH itself which is why Taylor standardizes their solution so that the net result of pH measurement is calibrated against their color comparators.

You can, of course, always add chlorine neutralizer to a sample if it has a much higher chlorine level and this is true for any test kit, not just Taylor's, but doing so can give you incorrect results due to the change in pH that occurs when the chlorine neutralizer (thiosulfate) reacts with chlorine.  Neither chlorine neutralizer solution nor its reaction products with chlorine are pH neutral.  Taylor is very clear about the potential interference of high sanitizer levels on their pH test so at least you can be aware of it and see the false color when the sanitizer level is very high.

As for the chlorine test, the FAS-DPD test is far more accurate than the DPD test where you can measure within 0.2 ppm if desired (using a 25 ml sample size; with a 10 ml sample size the resolution is 0.5 ppm).  See the demo link in this link.

Richard

[Micah]

[glow]The pH indicator solution in the Taylor test kit already has some amount of chlorine neutralizer in it[/glow] which is why you do not need to add any and the pH is accurate until the sanitizer level gets high,

This is my point.  The cheap $9.99 test kits all do exactly this.  For example "All Clear" make a 2&1 kit that retails for 5.99 and has the same P.H. testing method as the expensive Taylor kit. However if you move over to the 4&1 test kit from the same company they add chlorine neutralizer along with instructions that if chlorine levels exceed 3.0 then 2 drops of #4 are needed instead of just 1.

For the average consumer (not us chem geeks) it is far more important for them to have an accurate PH reading.  So many customers have come to me and said: "This PH decreaser sucks.  I have added 2 bottles and my PH is still way to high."  In nearly every occasion the chlorine level was over 3.0 thus giving us a false PH reading.  This type of a false reading is one of the most dangerous to consumers.  They think they are doing a good job when in fact they are damaging their heaters, pumps and sensors.  

[chem geek]

Maybe Taylor puts in more chlorine neutralizer than the cheaper kits, but I do know that I did some experiments with various levels of chlorine in buffered water (TA around 80 ppm) and found the pH test to be surprisingly accurate well above 3 ppm FC that you describe (but below 10 ppm).  I also found that using chlorine neutralizer had side effects on the pH -- not just on removing the color change from chlorine reacting with the indicator, but from the result of the dechlorination.

The instructions with the Taylor kit regarding pH are as follows:
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 purple 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 neuralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.
The Taylor kit comes with thiosulfate solution (R-0007) as part of the Total Alkalinity (TA) test so if you really wanted to use such a solution in the pH test, you could, though obviously that is not what is recommended by Taylor for the reasons given above.  If you know the chlorine level is very high, you can add thiosulfate and just recognize that it could still read high and not really be as high as you think.  However, very high chlorine levels, such as with shocking, are a temporary situation and when the chlorine gets used up the pH will be lowered by that process anyway.  The consumption of chlorine is acidic so trying to adjust the pH when the chlorine is very high doesn't make much sense anyway.  Usually, if you know you need to shock with a hypochlorite source of chlorine, you should lower the pH before making such addition since the added chlorine will make the pH rise and when it gets used up it will fall back down.  So to have the chlorine be more effective and to prevent scaling you lower the pH before adding a lot of chlorine.

For example, starting with pH 7.5, TA 100, CYA 30, adding 10 ppm Free Chlorine (FC) using a hypochlorite source of chlorine (chorinating liquid, bleach, Cal-Hypo, lithium hypochlorite) makes the pH rise to 8.0.  When the chlorine gets used up (i.e. drops back down to its original FC level) the pH drops back to 7.5.  If one initially lowered the pH to 7.3 before adding the chlorine, then the pH would rise to around 7.6 instead.

When you had the situations where you thought the pH reading was wrong and you found the FC to be above 3 ppm, how high was the FC?  If it was less than 10 ppm and you found a consistent problem, then you should contact Taylor about it.  I've done that before for other questions or concerns I had.

Richard

[EDIT] I did some more research and found that the major test kit manufacturers use a combination of chlorine inhibitors that are designed to work in conjunction to be of fairly neutral pH when neutralizing chlorine.  They also confirmed that using thiosulfate alone can lead to false high readings.  What is not so clear is the level of chlorine that is reasonably inhibited to not give a false reading -- it could be 10 ppm or 15 ppm.  It should be high enough to give reasonable pH results for most situations except high shock levels which, as I pointed out above, have a temporarily high pH anyway that will drop back down as the FC level drops. [END-EDIT]

[rubiconruby]

That may have been my problem then. I had been out of town for some time and there was no chlorine in the tub whatsoever. I will try to be sure there is at least a trace of it in there and then try testing.

[SpaWorldOnline]

Also worth considering is that high Cl/Br levels can bleach the Ph Pad/Reagent also giving misleading readings.

Also, the Ph pad is also the most susceptible to the SELL-BY-DATE!

I am have passed an ISPE course in chemistry and studied it for A level so I'd like to think I have an idea of what I'm doing, however I got into a real mess with my spa at home because the test strips were past their sell by date, and had to drain/refill it when I worked out what was wrong...

DPD is the way to go if u want real accuracy, but compared to a test strip, its a pain!

Commercial - use DPD,
Domestic - a good strip is fine.

I once stumbled across a UK co online who make a system that fits on the outside of the spa, with propes in the water. It gives an LED readout which indicates (without lifing the cover) if the Ph and Br/Cl levels are OK.  I heard the probes dont last long though...

[chem geek]

For real accuracy in a chlorine or bromine test, the FAS-DPD is the way to go.  It does not bleach out at high chlorine levels (the DPD test can make it look as if there is no chlorine when it's really > 10 ppm) and you simply count the drops so even someone who is color blind can do the test.  A demo of the test is linked to here.  The FAS-DPD test can measure accurately to within 0.2 ppm if you use a 25 ml sample or to within 0.5 ppm if you use a 10 ml sample.  The FAS-DPD test is in the Taylor K-2006 chlorine test kit you can get for a good online price here and in the TF100 test kit from tftestkits.com here with the latter kit having 36% more volume of reagents so is a little less expensive "per test".  For bromine, you can either use the chlorine test and multiply the result by 2.25 or you can use the Taylor K-2106 shown here.

Test strips only measure Total Alkalinity (TA) with an accuracy of 40 ppm while the above test kits measure TA within 10 ppm.  Test strips only measure Total Hardness (TH) which is irrelevant; they do not measure Calcium Hardness (CH) which is what is needed to know if you are at risk of scaling (usually due to high CH and TA fill water).

If you already have a drop-based test kit for pH, TA, CH, Cyanuric Acid (CYA), then you can get just the FAS-DPD chlorine test kit here or a FAS-DPD bromine test kit here though as I wrote above, you can use the chlorine test kit and multiply the result by 2.25 to get the bromine reading.

Richard