Low CYA breakpoint?

[don222]

Hi folks, I joined this great site several years ago and have often followed the various topics and always tried to follow your TFP methods. As a consequence I don't normally have any problems, it's a very rare occasion when I've had to slam the pool. I've always slammed to breakpoint as soon as I've noticed the chloromines getting over 0.4ppm but usually upping the dose to bring FC to around 7ppm once a week stops chloromines rising above 2ppm gets me back to zero, and up to now it's been a relatively short term painless exercise but it means I don't have any experience in longer term 'proper' slamming lasting for several days.

My current numbers are: CYA 20, FC 2.5, TC 2.9, PH 7.6, TA 108, CH 165.

CYA dropped low due to winter rainfall pump aways... normally I try to keep it around 32ppm. Prolonged periods of very hot sunny days in the UK aren't normally a problem and so far the low CYA hasn't been either. That IS gonna change but maybe ideal whilst I slam?

I test daily with DPD liquid regants and manually dose Liquid Chlorine to target FC at 4ppm. The FC demand seems to always be between 1.4-1.7ppm per 24 hrs giving a FC low point of 2.4- 2.7ppm no matter the weather. Although I've rarely had any problems, I'm wondering if I may have been sailing to close to wind and getting away with it and if I need to tweak those FC levels up slightly because I now have sure signs of algae!

I first noticed what appeared to be thin lines of dirt continually appearing roughly in line with the returns and small thin traces on the sloping walls of the deep end. I tried a sock in the skimmer when vacuuming (several times... but the 'dirt' kept reappearing within an hour of circulation starting up. At that time the chloromines were still close to zero. Then the water went slightly cloudy... chloromines leapt up to over 0.4ppm. Unfortunately we were then away for four days and although I upped the FC to 15ppm and also stuck a couple of large stabilised tablets in the skimmer basket... when we got back I noticed light green patches on the floor around the slope and deep end which came up into a nice green dust when swept! The FC was down to 5.5ppm - chloramines 0.4ppm... and realised I had a REAL problem starting up!

The questions I'm hoping you guys can answer for me are... what is the breakpoint for CYA at 20ppm?... I want (if possible!!!) to keep using the pool and realise slamming is gonna take several days as its now probably on the verge of getting worse!!! .. but would prefer not to keep TOO far past whatever it is so we can still swim!

Also... I can't run the pump 24 hrs due to neighbours beliving they hear a slight annoying hum when in bed!! The pump is in an enclosed brick building 10yrds away from their house with a high wood fence and high mature trees between... I don't see how... it's not especially noisy even close up... but there you go!

I intend to run 5.30 am - 11pm whilst slamming with a last check and dose if required around 8pm. So second question... can I get away with not circulating overnight?

I use liquid chlorine that is labeled as 14-15% sodium hypochlorite... but there is no other info or label on the container. It's what my local pool installers store supply... but other than using what I need to get FC to 4ppm I don't know much about it. I decant that into a 5gall strong plastic camping style water container with a tap on one corner and stick that on a shelf so I can fill into a small measuring jug. I dunno how to work out the volumes for a sloping wall vinyl pool but 20 fluid oz gets me from around 2.5 to 4ppm ok.

Wish we could get your recommended test kits over here but unfortunately it's not possible unless you guys go into the export business!

Sorry for the ramble... would love to get your thoughts, and grateful thanks for a brilliant & informative site.

 

[tim5055]

We don't recommend what I think you are saying, kind of a "limited SLAM" so you can keep swimming.

When we see a problem we believe in ketting it handled as soon as possible. That means following the directions on SLAMing your pool in the How To section of Pool School completely to the end.

CC is 0.5 or lower;
You pass an OCLT (ie overnight FC loss test shows a loss of 1.0 ppm or less);
The water is clear.
What you are proposing is just going to delay getting rid of the problem.

 

[don222]

Thanks for such a quick reply tim5055, I didn't mean doing a limited slam. I realise I have to get through the breakpoint AND keep it there to meet the three endgame conditions, it's just that I don't know the breakpoint I need to get to with the CYA so low at present.

 

[tim5055]

We always recommend bringing the CYA up to 30 before you begin a SLAM. With it below 30 you could end up loosing more to the sun than to the algae.

So, add CYA to 30 and SLAM to 12FC

 

[jblizzle]

I am not sure what this breakpoint you keep mentioning is, that is usually a meaningless term used by pool stores.

As Tim said, you want some CYA in the water to protect the FC from the sun during the SLAM process.

 

[don222]

Thanks guys, the breakpoint I was referring to is the CYA/chlorine oxidisation point as stated in Chem Geeks chart. I do realise the importance of normaly keeping CYA to at least 30ppm which according to the chart (means a breakpoint of 12ppm) CYA at 32ppm is where it normaly is and works just fine for me with only losing around 1.5 of FC per 24 hours. But the weather is such that losing virtually no FC to the sun is simply not a problem and won't be for the next week!!! so was hoping to know what that oxidisation point was with CYA at 20ppm. I'm loath to increase it till I've finished slamming but if you say I HAVE to in order to have a sucessful slam then so be it.

 

[tim5055]

Well, if you are going to keep it at 20, you just need to look at the Expanded Table to find your shock level.

For anything outside that posted, the math is at the bottom so you can figure shock level for any number.

 

[don222]

Thanks Tim, brilliant. I'd forgotten ChemGeek's expanded chart existed and was working from my copy of the simplified one. Thanks for pointing me in right direction. The number I was looking for is given as FC at 8.3. I can test regularly every 2-3 hrs so no problem ensuring daylight isn't eating the chlorine. I realise it can drop big time anyway when starting off slamming and I'll allow for that to start with... and then keep it around 10ppm till the three endgame conditions are met. Thanks again for your help.

 

[tim5055]

Thanks Tim, brilliant.

I would be patting my self on the back right now if family from your side of the pond didn't say brilliant all the time. I would just think you were talking about me

Glad it will work out for you.

 

[don222]

Ha ha! cheers then buddy and thanks again from not so sunny Bournemouth!

 

[chem geek]

Your CC readings you calculate from TC-FC from your DPD kit are NOT to be trusted. You should be using a FAS-DPD kit for testing FC and CC. I suspect that if you did so and used a 25 ml water sample that you would find that your CC is in fact almost always <= 0.2 ppm. You should not need to shock your pool as often as you are doing. I understand that in the UK you have trouble getting the FAS-DPD kit -- you should see if you can get the Palintest SP 300 FAS-DPD test kit.

You shouldn't refer to "breakpoint". What you are referring to is the Shock FC, but that is just a level primarily for quickly killing algae. It is not what you have to use to get rid of CC. The most effective way to reduce CC is through exposure to the UV in sunlight. Also, some types of CC are innocuous so if you don't smell "bad pool smell" and don't have other issues such as an unusually high chlorine demand or visible algae or dull/cloudy water, then I'd open the pool to sunlight and not worry about the CC.

 

[don222]

chem geek, thank you for your input. No wonder my terminology caused confusion! Your comments about CC are also very pertinent, I use a solar cover and the pool is probably covered over at least two days a week. It's gonna be nights only from now on! Thanks also for the Palintest info. I've scoured the web but unfortunately there doesn't seem to be any retailers for it other than from the states. I have found one full range FAS DPD testing kit by LaMotte which IS available and importantly backed up with replacement regants. That seems to be my only option and in view of your comments about even liquid regant DPD being unreliable that's the one I'll have to go for. Very greatful thanks for all the help you guys have given me.

 

[chem geek]

We have our cover on every day, but open the pool up almost every day for about an hour or two with some sunlight. Our CC is almost always <= 0.2 ppm. However, even if the pool is covered and not opened for several days, the CC is almost always <= 0.4 ppm. So I really wouldn't worry about your CC since I don't think it's that accurate in your test. If you don't have a "bad pool smell", I think you should do whatever you were doing with the cover. Just having the pool open and exposed to sunlight for the equivalent of one full day per week should be sufficient.

 

[don222]

Sounds good and thanks for your comments chem geek. Just to give an update on my problem. It took six days of following the TFT method of clearing up cloudy going on green pool water to get there, but after initially underestimating how fast chlorine got eaten up in the first couple of days and the need to test almost every three to four hours to keep up with it and stay just above the recommended shock levels I now have crystal clear water, only 0.3ppm overnight FC loss and 0.2ppm CC. I have now at last been able to increase the CYA from 20ppm to 35ppm and all parameters are staying stable. All is fine now and I have learned some important lessons... so very grateful thanks to everyone who gave their input and words of wisdom.

 

[tim5055]

Glad it worked out for you!!