Shocking the pool even though CC=0?

cheezedawg

Bronze Supporter
May 12, 2012
64
Elk Grove, CA
Hi all-

My water is clear and looks great, and the chemistry looks fine when I measure it (numbers below). But lately I have noticed a faint smell- a "pool smell" of chloramines or otherwise not very fresh that makes me think its not getting sanitized enough. I've asked my wife and kids if they have smelled it, but they don't really seem to notice it (like I said, its faint). Several times I have rushed in to get my Taylor test kit right when I notice it, but I always show adequate FC and no CC. My wife and kids are travelling for a few days, so I decided to take the opportunity shock the pool just in case, but I'm unsure if it will do anything. In the past I have only shocked when I had CC > 0.

A few things that might be relevant but might not be:
- Earlier this year in the spring, I misjudged my CYA level thinking it was higher than it was, and as a result I ran with low FC for a few weeks (FC of 1-2).
- There is one corner where on the tile up underneath the pool deck and out of the water, there is some calcium build up and what looks like green algae growing. This is all above the water line- I'm not sure if its an area just prone to splashing so it stays wet enough for algae to grow or what.
- We have a "Caribbean shelf" that is 15" deep or so, and the water gets warmer up there during the day when the pump isn't running. A few times when sweeping the pool this summer I've noticed a few small, dark dots on the plaster surface that take a little effort to sweep away. Don't know if that is algae or something else.

Here are the chemistry numbers from last night:
FC: Currently 18, normally run around 5 (SWG). I think I need to get it a bit higher for the shock. This was almost 2 gallons of liquid chlorine, which surprised me that FC wasnt higher.
CC: 0
PH: 7.8 (bringing this down to 7.5)
TA: 80
CH: 325
CYA: 70 or 80
Salt: 3450
Borates: 30
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
Hi all-

My water is clear and looks great, and the chemistry looks fine when I measure it (numbers below). But lately I have noticed a faint smell- a "pool smell" of chloramines or otherwise not very fresh that makes me think its not getting sanitized enough. I've asked my wife and kids if they have smelled it, but they don't really seem to notice it (like I said, its faint). Several times I have rushed in to get my Taylor test kit right when I notice it, but I always show adequate FC and no CC. My wife and kids are travelling for a few days, so I decided to take the opportunity shock the pool just in case, but I'm unsure if it will do anything. In the past I have only shocked when I had CC > 0.

A few things that might be relevant but might not be:
- Earlier this year in the spring, I misjudged my CYA level thinking it was higher than it was, and as a result I ran with low FC for a few weeks (FC of 1-2).
- There is one corner where on the tile up underneath the pool deck and out of the water, there is some calcium build up and what looks like green algae growing. This is all above the water line- I'm not sure if its an area just prone to splashing so it stays wet enough for algae to grow or what.
- We have a "Caribbean shelf" that is 15" deep or so, and the water gets warmer up there during the day when the pump isn't running. A few times when sweeping the pool this summer I've noticed a few small, dark dots on the plaster surface that take a little effort to sweep away. Don't know if that is algae or something else.

Here are the chemistry numbers from last night:
FC: Currently 18, normally run around 5 (SWG). I think I need to get it a bit higher for the shock. This was almost 2 gallons of liquid chlorine, which surprised me that FC wasnt higher.
CC: 0
PH: 7.8 (bringing this down to 7.5)
TA: 80
CH: 325
CYA: 70 or 80
Salt: 3450
Borates: 30
If your CYA is 80ppm, your shock level FC is 32ppm.

Can the pool pass an Overnight Chlorine Loss Test?
 

cheezedawg

Bronze Supporter
May 12, 2012
64
Elk Grove, CA
Dang- its a little more challenging to get it up to SLAM levels than I anticipated. I added 2 more gallons, which I thought would be plenty, but that only got me up to 25ppm. I just added another gallon and will check in a bit.

Does the FAS DPD test lose accuracy at high FC levels?
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
The FAS DPD test is accurate up to 50ppm.

If you have a good deep pink color, and a few undissolved crystals after you swirl you should be fine.

BTW - no need to raise to shock level if you are just doing an OCLT. Target range for your CYA (FC at 12-15% of CYA) is adequate for the OCLT.
 

cheezedawg

Bronze Supporter
May 12, 2012
64
Elk Grove, CA
Overnight chlorine loss was about 3ppm, so there is something going on. SLAM continues... My wife has a pool party scheduled for Friday, hope I can let the FC drop by then :)
 

AftonJeeper

Bronze Supporter
May 11, 2017
1,151
Twin Cities, MN
Remember that the pool is safe to swim in when you can see the bottom, FC at or below shock level for your CYA, and pH is between 7.2 and 7.8.

I normally bring my FC up to at least 10 for every party we have, my CYA is 40.