Dosing my pool with Cyanauric Acid

[SantiSuk]

I haven't dosed my salt chlorinated pool with Cyanauric for a few years - it has taken quite a few years for the level to come down to 40 from 70 - yes i know that starting level is higher than necessary (or is it?) since I read several years ago that levels above 30 add no appreciable sun degradation protection to the chlorine. But my starting point came from having dosed the pool manually with chlorine for a couple of years 3-4 years ago.

 

Anyway, having hovered around 40 ish for seems like 18 months I suddenly got my total chlorine levels dropping unusually quickly , so I accelerated my monthly CyA test and sure enough it had suddenly dropped to 32. Possibly the drop is a result of unusually high water temperatures in the last two weeks - it's been 2 years since I recorded 34 degree pool water temperatures. So time to dose with some CyA powder I bought a few months ago

 

So I googled for guidance on dosing methods, having established the quantity required to get me back up to 40*, and came across a series of "how to" videos, which in the nature of these things was a series of US pool companies saying broadly the same thing. The things that surprised me though from this collection were:

 

1. To a man they all commented as though you had a skimmer basket to pop the CyA into. I have an overflow channel feeding into a reserve tank
2. They used no protection when dosing and indeed one guy stuck his bare hands into the skimmer basket having poured in sludge and swished it around
3. One of the several clips advocated soaking the powder in a bucket of water for 24 hours. Others did not
4. One clip advocated pumping for 24 hours after dosing. Others either did not mention extra pumping and one advocated 5 hours
5. All seemed to reckon on levels of 30 to 50 ppm as being target which is not wildly out of my expectations but one added it should be 80-100 if operating a "salt system".

 

In view of impending holiday I had to crack on a bit this afternoon and made the following assumptions:

 

1. Soak the powder in a bucket of pool water overnight (15 hours) and will pour it into the channels to feed the reserve tank in the morning
2. Although it's acid it is nowhere near as acidic/corrosive/ dangerous as HcL. Nonetheless I did use chemical gloves and made sure I was not hanging over the powder when measuring out and stirring, so no breathing it in.
3. No harm in some extra pumping as I did a smallish dose of TA this afternoon, then pumped for 2 hours and added a medium dose of HcL for a further 3 hours of pumping this evening. So maybe I'll add a few more hours than my 6 hour normal regime tomorrow but can't see the need for 24 hours solid pumping
4. I'll ignore the 80 to 100 recommendation for a (presumably "salt-chlorinator system", which must have been what they meant) as being an outlier (and plain wrong?) recommendation. I've never heard that before and certainly Swimming Pool Thailand's dosing instruction on their plastic buckets goes with the norm 30-50 ish sort of recommendation with no singling out of chlorinator systems for additional reinforcement (or "conditioning as the Americans seem to call it)

 

Any experienced pool chemists out there think I should have done or should now be doing anything different? Oh and I'll take note of the recommendation they all made not to backwash for 2 days post dosing.

 

 

 

* I'm going to be away in Europe for a month so wanted all my chemical levels to move up from median to higher end of recommended ranges, to offer some protection against predictable fall-off while I'm away and while my pool will be under the care of a less competent pool boy (my BIL!) 

[Bagwain]

40 - 60 ppm optimum 50 ish ppm.

It doesn't work either side of those values! (End of story)

In fact it is counter productive over 60 ppm as it can cause chlorine lock!

No difference what type of system you use.

 

Best to dilute it in warm water 1st and spread around the pool whilst pump is on.

 

Make sure your Total Alkalinity is 120 ppm, Calcium 250 ppm after you final backwash before leaving!

 

Cheers

 

N

[SantiSuk]

Thanks a lot Bagwain.   In time to be useful too!

 

Good points about the TA. I normally dose mine up to 70ppm and redose when it hits 50, but it only takes 2-3 weeks to get down there in winter (curiously my TA levels seem to last longer in summer). No harm in dosing up to 100 though just to be sure). My calcium levels drift down very slowly and I keep it at 200 (now I've discovered that I had read bum advice that 100 is the optimal level and I worked it on that basis for 6 years!). I'll stick another 20 in for good measure.

 

[janclaes47]

4 hours ago, Bagwain said:

Make sure your Total Alkalinity is 120 ppm, Calcium 250 ppm after you final backwash before leaving!

 

Maybe you can explain how Alkalinity and Calcium levels are related to CYA effectiveness.

 

The Calcium in my SWG pool is ~ 250, while the TA is 50 ppm, and these levels stay constant for the past 5 years.

 

My experience told me that if I bring the TA higher, and then i don't even mention 120ppm, my pH levels become uncontrollable.

 

Now I have to add every now and then, and I mean maybe every 4-6 months, some HCI to lower the pH.

 

My CYA levels are below 50ppm, more like 30ppm,  by the way.

 

CYA doesn't evaporate, so hot water temperatures have no effect on CYA levels, and the higher your CYA level the higher your FC level has to be for the same effectiveness.

[Bagwain]

T/A & Calcium have nothing to do with CYA effectiveness.

 

T/A gives the water a stable & easier control of pH if between 80 - 120 ppm.

 

Calcium at the right levels stops the water being aggressive to the surface & equipment. However it does help slightly with Cl effectiveness if all else is in check!

 

As far as your experience - I have no idea of your pool & the state of it. If concrete is exposed in your pool (No grout or cracked tiles etc) you will have erratic & false reading as with many other possible scenarios!  Also how old are you reagents and do you keep in a cool place I.e. (Fridge)?

 

The guidelines I give are best practice for a standard no issue pool!! Salt or hand dosed!!