Factors effecting accuracy in CYA testing

algaeh8er

Well-known member
Jun 11, 2007
92
NorCal
#1
I had been operating my algae war under the belief that my CYA was at 70 PPM. This result was given to me by Leslie's and I also got the same result by doing my own test with the Walmart cheap kit. My pool was very cloudy when I got these results.

Now that I am about to declare victory in this war, I retested all of my numbers and I came up with a number between 30 and 40 for my CYA. So, is it safe to assume that the algae decreased the clarity of the sample and messed up the results on the earlier tests? (I haven't done any draining of the pool and I have a cartridge filter.) Also, if this is the case, then why would I have gotten a CYA result of under 30 when my pool was green and filthy?
 

The Mermaid Queen

TFP Expert
LifeTime Supporter
Mar 28, 2007
2,522
Northern KY
#2
Yes, that is a safe assumption. Anything that is clouding your water will have some effect on the CYA test. There is a thread here somewhere about that, I will try to locate it....
 

DavidD

Well-known member
Mar 29, 2007
91
#3
As The "Queen" has acknowledged, it is very likely and probably the main factor however another factor to consider is the loss of CYA due to the algae itself. Algae is known to break down CYA. I have seen this with my own eyes when after repeatedly warning a friend his CYA of 100+ was high, then an algae bloom set in. The next month, after we'd cleared the pool, CYA was 60. He had a D.E. filter so there were only two times in which the filter was "backwashed" and very little rain during the period. I remember Ben Powell (Pool Forum) always saying there are only two ways to lower CYA, draining and letting the pool turn into a swamp......

Dave
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
#4
Just to be technically correct, as far as I know it isn't algae that consumes CYA, but soil bacteria. However, when a pool gets an algae bloom, this usually means the chlorine has gone to zero -- perhaps it was low when the algae started, but then the growth of algae uses up all the chlorine. When the chlorine is near zero, bacteria can then thrive so with a little wind blowing in some soil bacteria into the pool, such bacteria can consume the CYA. This happens to many pools that are "let go" over the winter. When the bacteria consume CYA, it gets converted to ammonia and it takes a LOT of chlorine to break down that ammonia so the chlorine demand after opening a pool to green algae and CYA converted to ammonia is HUGE.

Richard
 

algaeh8er

Well-known member
Jun 11, 2007
92
NorCal
#5
I almost think it was better that I thought my CYA was higher. It took a lot of time for the pool to clear with the chlorine between 20-25. I can't imagine where the water quality would be now if I was keeping the chlorine levels lower. As it is, I'm still getting CC readings.