Stabilized Chloramine?

I have an I/G vinyl 25K gal pool which had an algae bloom about 2 weeks ago. I treated it agressively with bleach & cal hypo. It cleared up within 3 days of treatment. Pool is crystal clear but FC readings have stayed steadily over 10 since 6/27, despite no addition of Cl since then. This is using test strips since the Pentair test kit I have doesn't test past 3ppm, although I have ordered a FAS-DPD test kit.

My CYA is between 100 and 150, so I wonder if the FC readings I am getting is really a reading of CC? Does CYA also stabilize chloramines? The pool doesn't have a strong chlorine smell, so maybe the high CYA has kept the FC at such a high level? Should I shock now or wait until the FAS-DPD test confirms a high CC?

If you can bring the CYA level to near 80 ppm, you can get a better idea of what the chlorine can do. To my knowledge CYA has no impact on CC, other than being too high inhibiting the chlorine from working..

Once you get the test kit you will be in a much better position to give us readings that we can work and advise you.

Pat

The plus side to this is you've discovered the good side of having a high cya level , CL doesnt burn off that quickly. The only thing is with cya where it is you need to keep the cl where it is now according to the best quess chart

It's hard to tell without drop-testing, but if those numbers are right, things sound OK. Everything in pool chemistry is a balancing act.

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Originally Posted by njpool

My CYA is between 100 and 150, so I wonder if the FC readings I am getting is really a reading of CC? Does CYA also stabilize chloramines?

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Yes and no....When stabilizer combines with FC it forms a groups of compounds known as 'chloramides' such as chloroisicyanuric acid. These are a "combined chlorine" becuase the chlorine has combined with the sabilizer. However, these will test as FC, not CC, and have sanitizing and oxidizing ability...just not as much as FC. In the old days they used to stabilize chlorine by adding anhydrous ammonia to the pool to form monochloramine! (Some pool wholesale suppliers still sell anhydrous ammonia!) Monochoramine does have sanitizing ability and is a very good algae killer but it is short lived. It does possess more staying power in sunlight than FC, however. They also used to use sulfamic acid which formed chorosulfamates. Neither of these was as effective as cyanuric acid.
In short, stabilizers combines with the chorine and create what really is a form of combined chlorine. If you cya is beween 100 and 150 then you need a lot of FC in the pool to make sure there is some residual that has not combined or your pool will not be properly sanitized. My suggestin would be to lower the level of CYA by dilution (drain and refill) to get it into the range of 30-50 ppm.

Hope this didn't confuse you too much.