What's eating my chlorine?

[johnly]

I've noticed recently that more and more chlorine was needed to maintain FC. The water has been crystal clear since I filled it about a month ago. Chemistry has been right on other than allowing FC to drop below the minimum a couple of times. CC has never registered more than .5, and that's only been in the last several days.

So yesterday I decided to SLAM in order to get ahead of whatever might be in there. I accidentally brought FC to 25 (forgot to change values in poolmath). Anyway, last night it was 25, this morning it was 20, and now it's 15. Is this normal for water that's always been clear and never shown visible signs of algae?

FC 15
CC 0.5
TA 150
CH 275
PH 7.6 (before slam)
CYA 40

 

[JoyfulNoise]

I've noticed recently that more and more chlorine was needed to maintain FC. The water has been crystal clear since I filled it about a month ago. Chemistry has been right on other than allowing FC to drop below the minimum a couple of times. CC has never registered more than .5, and that's only been in the last several days.

So yesterday I decided to SLAM in order to get ahead of whatever might be in there. I accidentally brought FC to 25 (forgot to change values in poolmath). Anyway, last night it was 25, this morning it was 20, and now it's 15. Is this normal for water that's always been clear and never shown visible signs of algae?

FC 15
CC 5.5
TA 150
CH 275
PH 7.6 (before slam)
CYA 40

I'd repeat the OCLT again but if your FC loss is that high, you've got something in your water. Remember, here at TFP we have a saying -

CLEAR water is NOT a sign of CLEAN water!

or, to put is more succinctly,

Clear does not equal clean!

You likely need to SLAM.

 

[ned8377]

There are two things that lower chlorine, sunlight and algae/bacteria. If it dropped 5 ppm over night you have something.

 

[pooldv]

Yep, I had to SLAM last summer with crystal clear water and no CC. I had some algae growing in patches in the rocks/grout under the waterfall, some in the pool cleaner and some junk behind the light. I was also lazy about brushing last summer. Now I try to brush every week or two for sure.

 

[johnly]

Thanks for the replies. Yeah, this is one lesson I will learn only once. I just dislike brushing. Do suction side cleaners eliminate the need for brushing? If not, that's fine. I also dislike folding laundry, but I do it anyway.

 

[domct203]

I've noticed recently that more and more chlorine was needed to maintain FC. The water has been crystal clear since I filled it about a month ago. Chemistry has been right on other than allowing FC to drop below the minimum a couple of times. CC has never registered more than .5, and that's only been in the last several days.

So yesterday I decided to SLAM in order to get ahead of whatever might be in there. I accidentally brought FC to 25 (forgot to change values in poolmath). Anyway, last night it was 25, this morning it was 20, and now it's 15. Is this normal for water that's always been clear and never shown visible signs of algae?

FC 15
CC 5.5
TA 150
CH 275
PH 7.6 (before slam)
CYA 40

Have you been using non-chlorine shock (MPS)?

That CC 5.5ppm is showing that your chlorine is working hard to oxidize something .....

Dom

 

[johnly]

Oops, that CC should have been 0.5. And no, I've not used any pool "products" - following TFP to the letter. Very grateful to this site and it's contributors.

This morning's FC is 16, same as it was last night. I win!

 

[pooldv]

Nice! Good answer!