Under laboratory conditions these interferences might be significant but not to a home tester with a home test kit.
How about interfering with the CYA reading?
In the spring 1996 issue of the JSPSI Journal, Wojtowicz discusses the interferences in CYA testing. He suggests that if stabilized chlorine is used then "ideally the available chlorine should be reduced with thiosulfate prior to precipitation since some of the CYA is in the form of chloroisocyanurate" as the method has been calibrated for unchlorinated CYA solutions.
Prior to the chlorine reduction he suggests a 10 ppm chlorination (or using Oxone) to oxidize any oxidable materials that may interfere with the test - compounds such as uric acid may precipitate with melamine, for example.
But all this may be splitting hairs given the intrinsic precision (or lack thereof) of the CYA test.
Under laboratory conditions these interferences might be significant but not to a home tester with a home test kit.
Retired pool store and commercial pool maintenance guy.
LOL - you guys are talking over my head, but from reading all this, it sounds like I have nothing to worry about as long as the FC is below 10 when testing water?
Also, I purchased a new test kit from Leslie's pool store. It looks just like the Taylor 2005 test kit, but instead of a powder, it has R-0001 DPD Reagent #1 and R-0002 DPD Reagent #2. I add 5 drops of each. Just curious if one is better than the other. Seems like the powder would degrade faster than the drops.
The test kits says, "manufactured for Leslie's swimming pool supplies by Taylor Technologies, Inc. The number on the kit is 81-330. Its identical to my old 2005 except for the power that tested chlorine.
Leslie's numbers:
FC = 6 (I estimated it to be between 5 and 6)
pH = 7.7 (I measured 7.2)
TA = 100 (I measured 90)
CH = 175 (I measured 260 - note he used less water sample and less drops)
CYA = 80 (I measured ~65 - a test I hate because its so inaccurate due to looking at the black dot when it disappears).
Phosphates = 250 (I did not have any way to check this)
Salt = 2800 (same value I recorded)
The Phosphate issue for the last couple of years, I've been adding Phos Free to reduce it, but it increased my CH to the point where I had no choice but to drain ~ 75% of the water and replace it with fresh water. I don't plan to use that stuff anymore going forward for 2009.
So it sounds like you guys are saying to keep my FC around 5 to 6, even though the test kit recommends 3-4?
Reread the stickies at the head of each forum section, this one in particular:
http://www.poolforum.com/pf2/showthread.php?t=365
All the basics of good pool maintenance are basically contained in the stickies!
Last edited by waterbear; 02-06-2009 at 10:02 PM.
Retired pool store and commercial pool maintenance guy.
Leslie's DOES have the 2006 equiv. It's called the FAS-DPD Service Test Kit.
Carl
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