Help with sanitizing swimming pool water

M

mikefamig

Senior Member
Is there a swimming pool water technician in the house?
 
I have a 16' x 32' in-ground swimming pool. The water is clear and all of the chemicals are balanced except for one problem. I have a combined chlorine reading of 4 - 5 ppm. I have been maintaining a free chlorine level above ten for a few days now in an attempt to break up the CC but it is not working.
 
I started out with CC of 7.5 and was able to lower it by adding 4 gallons of 12.5% liquid chlorine and it did lower the CC to about 4.5. Now I don't want to bleach the vinyl liner so I have been adding 2 gallons of liquid at a time and maintaining free chlorine above ten but the CC is staying level at 4.5 for days.
 
Any help?
 
Mike.
 
First... I'm not an expert, but I do know a few things to help out.
 
What is your CYA level?
Also, your going to need to raise your FC level even higher as it's not able to control the contaminants at that level.
 
video321 - Thanks for the reply.
 
The cyanuric acid is ~50. I've seen arguments as to whether it should be around 50 ppm or closer to 100ppm and have foundthat the chlorine holds up well keeping it at or around 50.
 
I've read that it would take 10x the cc to break up the combined molecules which in my case would be 10x4.5 or 45 ppm. On the other hand I have read that raising the FC to ~15ppm and holding it there would do the trick.
 
I'm afraid to raise the chlorine to 50ppm for fear of bleaching the vinyl liner!
 
Mike.
 
I've calculated (based on 16,000 gallons of water) that 1 pint of 12.5% liquid chlorine will raise Free Cl by 1ppm. I also learned that at 50 CYA that my effective Cl is about 1/3 Free Cl. But I still have no idea what level my Free Cl or effective Cl needs to be to break up the Combined Cl.
 
So how high must I raise the Free Cl in order to break up 4.5 Combined Cl at 40 - 50 CYA?
 
Mike.
 
If your cya is around 50 then you should be able to shock around 20-25. Give that a try and see if it works out.
 
Do you have a SWG? If so, then a cya of 50 may be the minimum. If not, then a cya of 30-50 would be ideal. You don't want to go any higher than around 70 in either case.
 
If SWG is "Salt Water Generator" then no. I use either the Sustain chlorine system or just liquid chlorine. This year we started with Sustain.
 
I shocked hard yesterday and currently have the free Cl around 20 or better. It is pouring rain right now and I am going to let the chlorine drop back to safe swimming level and see what is left for Combined Cl at that point hoping that the rain will dilute it a little. Then if the combined is still high I will start all over again with a hard shock as you suggest. My wife wants to swim on Sunday and the pool has been at Cl levels between 10 and 20 for four days now. I think that it is a good idea to let the Cl drop and test and adjust the Ph before continuing. High Ph has a negative effect on chlorine's effectiveness.
 
When I first noticed the high CC it was at 7.5. I added 3 gallons of 12.5 Cl and two cups of 65% Sustain shock and the CC dropped to 4.5. Now that it is at 4.5 it seem simpossible to get it any lower. Maybe the Ph is the problem.
 
So I feel like I'm between a rock and a hard place. Shock too high and damage the liner or shock too low and increase the CC.
 
Do you have a vinyl liner? How high have you shocked it? Do you have any clue how high is too high for a vinyl liner?
 
video321 said:
If your cya is around 50 then you should be able to shock around 20-25. Give that a try and see if it works out.
 
Do you have a SWG? If so, then a cya of 50 may be the minimum. If not, then a cya of 30-50 would be ideal. You don't want to go any higher than around 70 in either case.
Click to expand...
 
Am I correct that my goal is to bring the "effective" Cl to a level equal or greater than the combined Cl in order to break the Combined Cl?
 
In other words,
if FC=25 and CYA=50 then it should yield an effective Cl >=4.5 Combined Cl?
 
I have a swg and keep my fc level 1-2 ppm higher than what is needed for my cya level. I just checked my CC this afternoon and it shows as anywhere from 0 to less than .5 - I should have tested for .2 increments. Anyway... if you don't stay on your CC then it will start to rise again - keep the fc level up!
 
As for your liner, again no expert with NO liability, I'd think you'd be fine with the high levels. Just don't pour any directly on the liner, pour slowly in front of a jet and keep the pump running. The concentration is very low after its mixed in with the water.
 
Oh and that sustain shock - check to see if its adding cya with it. I wouldn't use it if so.
 
You can also try posting over at https://www.troublefreepool.com
 
Good luck to you!
 
No the Sustain shock does not contain any stabilizer.
 
I had my FC up to 20 yesterday and added two cups of the sustain 65% dry chlorine so I probably reached about 25ppm after that. For some reason it is just not bringing down the CC. Maybe the Ph has gotten too high for the Cl to be effective.
 
I have been reading at troublefreepool but haven't joined yet so I can't post there. Like I said I'll let the chlorine fall to 3 - 4 and adjust the Ph  so that wife can swim on Sunday and go from there next Monday.
 
Thanks for shedding some light. I still don't understand why the CC didn't drop with the amount of chlorine that I threw at it. I have  a newTaylor dpd-fas test kit and trust it's accuracy.
 
Again I think that the Ph must be through the roof after all of the Chlorine all week long. I'll adjust and start over.
 
That's what I use for testing chlorine. You should definitely test your ph. You're right that if it's too high then the fc effectiveness drops off.
 
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