What to believe

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belgique

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Jun 16, 2009
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Cedar Island NC (Outer Banks)
The pool is almost there...I still get some clouds of brownish/green when I sweep but way down. Still a little cloudy, can can see the bottom. I sweep several times a day. It is holding FC pretty well...never drops below 12. Not stable enough yet to do the overnight test.

I'm surprised that after almost 2 weeks of keeping it at shock, I still get the residue. Last week I did my tests using the cosmic test kit and took a sample of the same water to the pool store...the lady is a friend. well experienced and doesn't try to sell me stuff. The first numbers are my readings; the 2nd are the pool store's using their computer. Note the HUGE FC difference! Back home a strip says mine or more likely. But, why do I still have algae after almost 2 weeks?

The 3rd set of numbers are what I just did...in all my tests, I was very careful and the FC used fresh powder. No significant rain or fresh water added.

Me Store Me today
FC: 12; 5.8; 12
CC 1; 6; unk...out of chem
PH 7.8; 8.3; 8! (It was 7.4 two days ago)
TA 300; 253; 300
CH 240; 283; 275
CYA 60; 45; 35

Assume:
Keep sweeping
Keep it at shock
Get Ph back down

Suggestions? Thanks, Steve
 
Test strips are not reliable and many of the systems pool stores use to test are also not reliable. Is the store using a system with a test strip read by a computer (not good at all) or do they put pool water into vials which are read by a computer (better but not perfect)?

FC can go away on the way to the pool store for testing. FC levels can change from both sunlight and evaporation in different ways in a small container than they do in the pool.

If CYA is actually 60 and FC is actually 12 then your FC level is not high enough to reliably kill all the algae. It is also difficult yo kill algae if your PH goes too high, though that can be difficult to determine as most of the PH tests get unreliable at high FC levels.

By far the best thing you can do is to get your own top quality test kit. Reliable numbers available any time you need them makes a huge difference. I recommend the TF100 from TFTestKits.net. The Taylor K-2006 is also good.
 
All of the tests agree that your TA is very high. PH tends to go up, and can sometimes go up quite quickly, when TA is that high. Basically high TA and aeration will raise the PH. Rain is one possible source of aeration.

The next time FC is below 10 you should lower the PH down to around 7.2.

The difference in the CYA test is more problematic. The CYA test is somewhat difficult to do consistently. For example many people report getting lower levels in the evening and higher levels when reading in sunlight. The CYA test was designed to be done in direct sunlight facing away from the sun so that the view tube is shaded by your body.

If CYA is 40 you want FC up to at least 15, and if CYA is 60 you want FC up around 18 to 24. Until you get more information about what the CYA level really is, I suggest raising FC up to the 18 to 20 range.
 
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