Woodlands Texas Pool update: All is well!

[cwuffman]

I generally learn more by reading forums than by posting, but thought it was time to report in.

As previously mentioned on this forum, I had drained 2/3 or more water to reduce CYA from 130 to acceptable. My after drain CYA level was 20 or less according to my TF-100 kit. Just for comparison my wife took a sample to the most reliable local pool store and they tested the water at 30. I decided to raise my <20 number to approximately 30-40 using trichlor tablets. We had to go out of town anyway so it was a convenient time.

Pool is now crystal clear and no sign of algae. The latest numbers with the TF-100 are:

FC- 2-4 generally
pH: 7.5
TA: 80
CH: 280
CYA: about 30

Now here is where I would like some input. My wife and I are both wondering about the true level of CYA. It seems to both of us that we can nearly always see the black dot in the tube. Again out of curiosity we took a sample to the above mentioned pool store and were measured at 45 ppm CYA. They are consistently measuring us 10-15 ppm higher than our TF-100 kit seems to indicate. I know both numbers are acceptable, but I would like to know how accurate I can expect to be so that I know when I have flexibility to use trichlor tabs while we are out of town. I have found (as most folks here have) that a little trichlor goes a long way.

Thanks in advance for your answers.

 

[Christian]

Hi Carl,

Pool stores often don't clean out their testers after each use which can lead to high readings because of the residue left over from previous tests. I would trust your TF-100 over a pool store!

 

[UnderWaterVanya]

Are you testing with your back to the sun and at waist high?
Are they?
Typically if they test indoors they will get results LOWER not higher than yours should be.

However the test has a +/- 15ppm error band. What this means is that you do your best to get the exact number and you work from there. The levels are conservative enough in the charts to allow for this from what I understand - I asked that question a few weeks back.

 

[cwuffman]

I believe they (Leslie's pool supply) use some type of electronic gadget, but I could be wrong. I hold the tube about waist high in a shady area away from the sun. Maybe I am making too big a deal out of this. It would be nice to be able to compare observations in person with another experienced BBB person.

Thanks again for comments and assistance.

 

[anonapersona]

You might try "back to the sun" instead of in a shady area, see if it alters your results. I did it inside for a long time before I realized that inside vs in the sun was so important.

Before you assume that the difference is significant, give them another sample or two, and see if they are always higher than your value. If they vary a lot from day to day or week to week, then their repeatabilty is suspect, and we know that CYA does not change very quickly on it's own. I will be interested to see if, should you walk in the following day and ask them to test again, maybe tell them you added something if anyone asks. Then see if they show a change when since you did nothing, it should be exactly the same as before.

 

[cwuffman]

I mentioned this before, but at a different pool store I had the refilled pool water tested by one of the managers at 30 ppm. A week later after adjusting TA and adding NO CYA, I had them test it again. This time a young employee told me I had 65 ppm CYA. It's become VERY entertaining to go to the pool store, as long as you know what you are doing.

It's also interesting to get good test results from the pool store and then receive a full page recommendation of other additives that you "should" be adding on a regular basis. Incredible! Crystal clear water, no algae or other contaminants, good test results in all necessary parameters, and you still need to buy more stuff!

 

[duraleigh]

Standing outside, back to the sun, ALWAYS trust the results of your own testing. YOur results may come in somewhat lower (less CYA) than if you test outside. It's a subjective test but you will always be better than the pool store.

 

[Pauls234]

I had similar questions about CYA testing and got a lot of good insight.

cya-testing-just-disappears-seems-subjective-t50754.html?hilit=cya test subjective

 

[march2012]

I generally learn more by reading forums than by posting, but thought it was time to report in.

As previously mentioned on this forum, I had drained 2/3 or more water to reduce CYA from 130 to acceptable. My after drain CYA level was 20 or less according to my TF-100 kit. Just for comparison my wife took a sample to the most reliable local pool store and they tested the water at 30. I decided to raise my <20 number to approximately 30-40 using trichlor tablets. We had to go out of town anyway so it was a convenient time.

Pool is now crystal clear and no sign of algae. The latest numbers with the TF-100 are:

FC- 2-4 generally
pH: 7.5
TA: 80
CH: 280
CYA: about 30

Now here is where I would like some input. My wife and I are both wondering about the true level of CYA. It seems to both of us that we can nearly always see the black dot in the tube. Again out of curiosity we took a sample to the above mentioned pool store and were measured at 45 ppm CYA. They are consistently measuring us 10-15 ppm higher than our TF-100 kit seems to indicate. I know both numbers are acceptable, but I would like to know how accurate I can expect to be so that I know when I have flexibility to use trichlor tabs while we are out of town. I have found (as most folks here have) that a little trichlor goes a long way.

Thanks in advance for your answers.

you can retest the same sample over and over by pouring it back into the mixing bottle and running the test again. AFter 5-6 times of running the same sample you should get an idea of where you are really at. Also the dot should go away completely.

 

[anonapersona]

I will point out that the black dot must disappear, not the paper that the dot is on. For some time I was not aware of the difference. Standing in the sun, I get some reflection off the pavement and used to wait for the entire larger paper to be obscured. Finally I began looking to see when I could not tell if it was a circle or an oval or a square, not that there was nothing at all in the bottom of the tube. That way I was not fooled by the larger round paper itself.

 

[cwuffman]

Since the issue of misinterpreting the white circle for the black dot seems to come up so regularly, I wonder if maybe the black dot could be changed to a black square, or triangle?? Just a thought! Maybe a dumb one.