Need to shock the pool AGAIN

[uzun]

I posted about a month ago a problem I was having with my SWG not being able to keep up. I needed to properly shock the pool, which I did. I have been closely monitoring the FCL levels since then, and in the past few days I notice they have been dropping, they held steady for about 30 days. I did the overnight test last night and the pool went from 3.4 to 3.0 FCL overnight. Clearly I need to shock the pool again.

Why would I need to shock the pool again just a month after I shocked it before? This can't be normal. I even have been adding the "magic powder" (oxidizing shock, potassium monopersulfate) every week or so to try and avoid this.

I noticed about once per 7-10 days the water would get very slightly cloudy. A light milky haze that you could only see with goggles underwater when you swam. When it got like that I would add the Oxidizing Shock and it would go away.

Is something happening to my water to make me have to shock it like this? For about 30 days the chlorine levels were fine with the SWG at about 30-40% for 5 hours a day.

-Roger

 

[dattia]

I may be wrong, but a thought a drop of 1.0 drop during the OCLT was the general rule for taking action. Your drop seems to fall within a normal range.

 

[Richard320]

If you only lost .4 FC overnight, you passed the overnight test. Why do you feel the need to perform the shock process? Can you post a full set of test results? Note: if you added any MPS, you'll need to wait a couple days, as it gives falsely high CC readings.

A good heat wave, a lot of use, even a lot of wind blowing dust in can all lead to increased chlorine demand. If you're consistently testing and maintaining FC levels, you'd be on top of it. Nothing is set-it-and-forget-it; that's why the SWG lets you adjust the percentage.

As an aside, you're throwing money away buying the MPS. If the FC level is maintained above the minimum you shouldn't ever need it.

Start with a full set of test results, and tell us what tester you used. We'll get things sorted out.

 

[BoDarville]

I did the overnight test last night and the pool went from 3.4 to 3.0 FCL overnight. Clearly I need to shock the pool again.

Actually, you don't based on this result. You lost only 0.4 ppm FC. If you had lost more than 1.0 ppm, then you would need to shock. Refer to OCLT.

I even have been adding the "magic powder" (oxidizing shock, potassium monopersulfate) every week or so to try and avoid this.

There is no need to use these products. Simply maintain the proper FC for your pool's CYA and you will be fine. Make sure SWG is working properly and adjust output and/or run time as needed. Use plain unscented liquid bleach if supplemental dosing is necessary. I haven't shocked my pool in nearly 2 years. It is really this simple...don't try to over-think it.

Edits in red

 

[uzun]

Prior to this week it would drop 0 overnight. So the drop of 0.4 is new but perhaps within normal? I also have to raise the SWG level this week to keep up which I've not had to do before.

Looks like this is within normal though. I have not added oxidizing shock recently, not with 2-3 days.

Roger

 

[BoDarville]

Prior to this week it would drop 0 overnight. So the drop of 0.4 is new but perhaps within normal?

Correct. The OCLT can fluctuate a little even when your water is clean, but you are still well within range.

I have not added oxidizing shock recently, not with 2-3 days.

Wouldn't add any more. Focus on testing and maintaining the proper FC and adjust SWG as necessary.

 

[dattia]

It is great that you are keeping such a keen eye on your pool... that is the basis of the BBB method, after all. Know your pool! Even though you are still in the normal range for the OCLT, you have noticed a change. As mentioned above, there can be many reasons for a change in the chlorine demand, but it isn't necessary to shock at all right now. I also would stop using the Magic Powder. It really isn't necessary. You can bump up your FC a little if that makes you more comfortable. Do you have any CC's, is your water clear?

 

[Isaac-1]

What are you calling "oxidizing shock"?

 

[uzun]

Oxidizing shock is Pottasium Monpersulfate as per the initial post. I already added a ton of bleach and some of the chlorine shock to the water, and it became slightly cloudy. I guess I will just run the filter a bit more, turn off the SWG and keep the pool uncovered so I can swim in it again soon. I jumped the gun on the shocking having not read and realized it needs to fall more than 1.0 to need shock.

The pool has been very hot, over 92 degrees, and there is a layer of super heated water underneath the cover that forms every day. I swim in the morning and leave the pool covered all day. Maybe leaving it covered is a bad idea on summer days I dont know. I have one of the motorized pool covers that are a dark, thick canvas material.

I use the potassium monpersulfate when I notice it getting a bit milky, that clears the water right up and I was hoping it would sort of "mini-shock" the pool and free up any chlorine.

The combined chlorine readings this entire time have generally been 0, but have occasionally been 0.2 or 0.4. For the most part 0.0

-Roger

 

[RobbieH]

Why not use the 10 ml sample size for testing instead of the 25 ml?

 

[uzun]

Ive been keeping close tabs on the FCL levels so I use the 25ml sample so I can follow it more closely.

 

[Patrick_B]

Ive been keeping close tabs on the FCL levels so I use the 25ml sample so I can follow it more closely.

You get better resolution with a larger sample and that is just a fact of performing "wet testing". I like accuracy too, but honestly you can save yourself a lot of reagent and still get all the resolution you need for FC/CC. Just saying....