Test results vary between meter and drop test - not sure what to do?

[waterbear]

If you are going to believe a salt test, then the drop based Taylor K-1766 is the one to use. It beats any meter that I have come across, especially from a pool store. It is a gimmick that has to be calibrated frequently, and as such I consider it a copout for serious testing.

Apologies for the rant, but things like this push my buttons.

Pat

You are correct abot the meters needing frequent calibration which is why we calibrate our Goldline salt meter weekly! It is off about every 4-5 weeks. (We don't really use the MyronL TDS meter because we feel that TDS readings are not important...we still calibrate it monthly.)

[waterbear]

I just bought a salt test kit today and tried it out. I had been thinking the aqualogic was reading high because when it was showing 3200 early in the year, I took the water to the store and they read 2900. Around the same time, I tried a salt strip and it showed around 2900, so I assumed the aqualogic was high.

Today, I took a sample to the store when I bought the Taylor salt drop test. They read 2900 with their probe. The aqualogic is reading 2800. I just tried the drop kit for the first time and it took 16 drops. Ugh! Just the opposite of what I expected. I'll try the drop test again this weekend and a test strip also. Maybe I'll take the water in to another store too. I'm not sure what to believe at this point. I guess I'll trust the aqualogic for a while and do some more testing.

For my test, getting to drops 13-15, the drops would go in, turn the entry point red, and the solution would go back to all yellow. It was the 16th drop that all of a sudden turned the entire solution red (light brown) and it stayed that way.

Robert

So that means you are reading 3200 ppm. That is not very far off from your aqualogic...It could be due to temperature difference since the aqualogic measures conductivity to determine salt level (and so do some meters) and temp can cause the reading to be low or high. I see about a 100 ppm difference in my pool and a 300 ppm difference in my spa with the readout on my aqualogic vs. Taylor salt test (still waiting on resolution on Ben's test) , Aquacheck White salt strips (which are ususally within about 100 ppm or less of the chemical test because of precision limitations of the strips) and the goldline meter we use at work (usually spot on with the Taylor test and very close to the strips.) I don't lose any sleep over it.

Remember that the precision of the Taylor test is 200 ppm. It means that there is a plus or minus variance of 200 ppm over the reading you get. Within that variance your test could be 3000 ppm or 3400 ppm. 2900 ppm tested with a meter and a salt strip and 3000 determined by a chemical test are close enough for government work!

[rpoldervaart]

Thanks Waterbear. I was wondering about tempurature effects too. I have the pump suction to about 80% skimmers and 20% bottom drain, so it's probably getting fairly warm water off the top. When I test the water, I fill a test bottle from as far down as my arm can reach, so it's probably a bit cooler than what the skimmer picks up.

Sounds like it's all within a tolerable range. At least now, I have strips, drop test, and the aqualogic, so I'll occasionally test all three to get a general feel for where things are at.

Thanks,
Robert

[PoolDoc]

Just a couple of general comments;

1. I think -- but haven't proved via test standards sent to customers -- that the current version of the salt test is reasonably accurate.
2. "Reasonably accurate" is subject to interpretation from several angles. The test capability is + / - 200 ppm with a 3 ml sample, which I can achieve in my own testing here against a standard. My guess is that field testing, by a wide variety of users may vary +/- 400 ppm (2 drops either way) as a result of technique. This is "reasonably accurate" from the point of view of the test itself. However, as best I can tell, it's also "reasonably accurate" from the point of view of SWG operation, which is to say that the SWG will work alright if you are are supposed to maintain 3200 ppm, and are doing so with my test, but really (due to both intrinsic test variation and technique problems) have either 2800 ppm or 3600 ppm.
3. I'm going to ship complete replacements for the salt test in the first few kits (including WaterBear's) next week. The original version sucked, for a variety of reasons. The reagents are OK, and can be saved.
4. I may be able to begin sending out standard test samples as well about that time. I'm very interested to get better data on how my test . . . and other people's tests . . . perform for a variety of users against a standard.
5. It's been a long summer in the tunnel here, but I think that's daylight I see off in the distance .

Ben

[west1745]

You are correct abot the meters needing frequent calibration which is why we calibrate our Goldline salt meter weekly! It is off about every 4-5 weeks. (We don't really use the MyronL TDS meter because we feel that TDS readings are not important...we still calibrate it monthly.)

How do you calibrate it?