Printable View
I tool a sample to Leslie's and they said my CYA was 70. I did the test at home using Ben's kit and saw closer to 30. Why such a large variance?
I plan to take a sample to another pool store soon to see what they come up with.
My SWG instruction says to hold CYA at 60-80 so depending on who is right, I either need to add some or am right on target. I added 2 lbs about 2 weeks ago since this is a new fill .
Any reason I should be gettng such a variance?
CYA tests are not the most accurate tests!!! I would trust yours. Assuming you did the 7cc/7cc reagent pool water test.
I had a similar discrepency come up when measuring Calcium Hardness (CH). The pool store said I had 350 while my Taylor K-2005 test kit said I had 250. I got another fresh batch of chemicals from Taylor just to be sure and got the same results. I also tested my tap water and got the same results as my water company published (though had to do some conversions of the units and magnesium/calcium ratios). I've never trusted the pool store since.
For the CYA test, remember that the appearance of the black dot has to completely go away. There is a thread I saw on this forum that I can't find anymore that discusses some of this along with some photos. Since the SWG system is at its highest efficiency when the CYA is at 60-80, you should see that you can lower your power level and/or percent on-time to get the same chlorine level (FC) at the higher CYA.
Richard
thanks...
I'm going to get a few more test done as well as perform mine again. Since mine is coming out low, I'd hate to add more and then find out it was already high enough.
Original test showed 0 on my test and 20 at the pool store. I added 2lbs which should have brought it up to more than the 30 i came up with .
How are you figuring that adding 2 pounds of CYA to your 20,000 gallon pool will raise the CYA to 30? I show that you have to add quite a lot more than that. For a 20,000 gallon pool, it would take 10 pounds of CYA to add 60 ppm. Of course, you should add less and retest since as you point out you don't want to go over since that can only be corrected through a partial drain and refill.Quote:
Originally Posted by Phillbo
If you add 2 pounds, this can raise the CYA by [EDIT] 12 [END-EDIT] so that could be raising it from the 20 measured at the pool store (which you thought was 0) to 30 that you measure now. At any rate, I would just use your measurements which now show 30. Add half the required CYA to get to 70 so that would be about 3.5 pounds, then retest to see that you are at around 50, then add some more. Be sure to wait for circulation in your pool -- at least an hour.
P.S.
How could your original test showed 0? The most common test only has a scale that goes to 30, though some go to 20. If you fill the water to the top of the tube, then you know the CYA is less than the last line near the top of the tube, but you can't really tell how much less.
Richard
When the pool store tests for CYA, make sure that they clean the tube with the black dot. If they don't then don't accept their reading. That is why I do my own testing, and it is painstakingly consistent.
Remember too that the way they do it, is highly likely different from the way you do it.
Pat
someone posted on here in the worst pool store story thread that sounds like it might be what is happening in your case!
http://www.poolforum.com/pf2/showpos...2&postcount=27
You are testing 30, they are saying 70.....100-30=70! Sounds like the training at one of the larger pool store chains leaves something to be desired!