K-2006 Vs. Pool Pro

[PDub]

I wish I would have done a test right before I went to the pool store but I did test last night 8:00pm and had the pro test at around 2:00pm today. The problem I'm having is the free chlorine test. My test was 5.4ppm their test today is 2.9ppm with a total at 3.7.

Everything else seems close. They use a Bio-Guard test strip system connected to a computer. I'm wondering if I'm using the powder wrong or something. They are calling for shock if the level is indeed 2.9. I have shock. What is the max chlorine that is swimmable?

[pl321]

I went home right after work a did a test and it was 3.8. One thing I remembered is that my filter timing my have played a roll. It turns on at noon and off at 8:00 pm. So the SWG would only have been running a couple of hours before I took the sample to the Pro. Could the FC drop that quickly from 8:00 pm to noon while the SWG is off? I'm going do some testing tomorrow and maybe take a sample to another store that uses vial system. Trying not to use up all my powder in the process.

[PDub]

Sorry all, I'm not sure how I ended up with two logins at any rate it rained here Saturday and I wasn't able to do the side by side test yet. I'll get back to you. I plan on testing the water myself and then taking two samples to two "Pros". One with strip testing (bio-guard system) and the other Pro has a system called "Pinpoint" or something like that and it's a Vial system and we will see what we get. I like to take my water and have it tested before the week end. The trick is to get out of there without them selling me anything.

PDub

[chem geek]

Pool stores vary a lot in the reliability of their testing. You can read about some people's experiences here and here.

[PDub]

Good threads. Thanks for the links CG. I think I'll stick with my K-2006 readings from now on.

I can't say that I really like the test strips. They used some manual test strips to test my salt level and I know that was way off from my meter. Anyways it's all good my pool is clean and safe.

Is there a good Salt test that I could check against my meter reading every now and then?

[chem geek]

The AquaCheck White salt tests seen here are an accurate test strip. The Taylor K-1766 drop-based test shown here also works. I have both and they measure close to each other. You can use a larger sample size on the Taylor kit and then scale accordingly for more accuracy though the endpoint won't be quite as distinct.

Richard

[PaP dude]

I use a dissolved solid meter to test salinity of water. Is this a fairly accurate way? (It is calibrated often with a stock solution)

[chem geek]

Most of Total Dissolved Solids is sodium chloride salt in a saltwater chlorine generator (SWG) pool. However, in a non-SWG pool, the salt is mostly calcium chloride and sodium bicarbonate so the TDS number is only a rough approximation in that case.

Does your meter (which measures conductivity) reference a certain level of Calcium Hardness (CH) and Total Alkalinity (TA) or use stock solutions with the same CH and TA as in your pool? If so, then it can very reasonably approximate the chloride level which is really what you want to know for an SWG pool anyway (the sodium doesn't matter -- the salt could be calcium chloride or even potassium chloride and the SWG would work just as well, assuming the calcium wasn't so high as to promote scaling).

[PaP dude]

I am assuming it measures directly the amount of sodium chloride salt (or at least i thought so anyway )

I use the dissolved solid meter shown here. (This link isn't working for some reason but it is the Myron L Pool Meter)

I don't really know how it works (if you could tell me, it would be nice) but it usually gives me pretty close results when comparing with test strips that test for sodium chloride. Is my ds meter testing for how much of the chloride ion is in solution or does it some how isolate sodium chloride?

I guess that when it comes to pools that use an electrolytic cell to chlorinate, the chloride ion is really what matters. It gets oxidized at the anode to form chlorine gas. The sodium ion is more so a spectator ion since the water molecules are being reduced at the cathode. I would have to agree with you that the salt doesn't matter weather it be sodium chloride, calcium chloride, or even potassium chloride.

[chem geek]

Your meter is probably this one which just measures conductivity of the water. According to this document, the TDS 442 standard your meter calibrates to is composed of 40% sodium sulfate, 40% sodium bicarbonate, 20% sodium chloride (all diluted in water, of course). When you get a TDS measurement, it is relative to this standard. When you ask for a sodium chloride salt measurement, it gives you the equivalent concentration in salt for that same conductivity.

So basically if you set it to read using the "N" setting for sodium chloride (NaCl), then this will be approximately correct for high salt pools such as those with an SWG system. The error will come from the fact that some of the conductivity for negative charge will be bicarbonate instead of chloride and some of the conductivity from other ions has a different equivalent conductivity than chloride ion.

For example, in pool water with 100 ppm TA, 30 ppm CYA, 300 ppm CH that was created mostly from sodium bicarbonate and calcium chloride, the TDS is 526 ppm, the salt level is 350 ppm and the conductivity is 0.999 mS/cm. However, equivalent water with just 350 ppm salt and no TA or CH or CYA would have a conductivity of 0.755. Or put another way, if you measured standard pool water with your meter, it would say there is 463 ppm salt when it's really 350 ppm.

The error with SWG pools is much less percentage-wise. When the salt level is really 3000 ppm in standard pool water (except for the extra salt), your meter will measure it as 3113 ppm. So this is not very much of an error -- it basically reads too high by 113 ppm mostly due to the 100 ppm TA from sodium bicarbonate that it counts as if it were salt (sodium chloride).

Richard