CyprusLiving

Please help my (mis)understanding!

Note: I have read the posts here mentioning cyanuric acid; they do not relieve my quandary.

I understand from the extensive and detailed literature online that cyanuric acid (CYA) concentrations inevitably increase, whatever method of introduction is used (direct/dichlor/trichlor).
Also, there seems no chemical way of reducing CYA concentration (though there are chemicals with refuted efficacy), hence the common recommendation to part-drain a pool to reduce overconcentration of cyanuric acid.

I am looking for confirmation that is really the case. That is, if using chemical means of sanitizing a pool:
- one uses chlorine (hypochlorous acid one way or another),
- and one needs to use cyanuric acid (direct/dichlor/trichlor) as a stabilizer (or accept dosing daily to replenish chlorine),
- and then one will inevitably have to part-drain the pool at some time (hence incurring cost of water replacement, probably by bowser).

I find it surprising that many pool owners that use chemicals for sanitization will have to go through this, and most seem unaware of it.
If it is true, how many years might it take between such partial drainings?


I am asking because my pool has this problem (I know because of testing and because we have the purple line problem (copper cyanurate)).
And it is not because I have been overdosing: we use trichlor multitabs (made in Spain) and put new ones in (one per skimmer) only when the old one has dissolved. (One has to presume the tabs themselves are correctly balanced in terms of chlorine/cyanuric acid.)


Confirmation / refutation / comments appreciated, thanks.

JB,
Thanks

I had a good old browse there, learned one or two useful things, eg.
- confirmation that we are using the 'best stuff' in using 90% trichlor from a European company in sealed (not re-sealed) tubs
- use rainwater to top-up pool, as a means of flushing cyanuric acid and avoiding dodgy tanker water

But nothing that really answers my question.

I have posed my question to a couple of pool-related companies; I shall post here when/if I get useful replies.

OK this is one of my "big things"...
Cyanuric acid is used as stabiliser, as it is the most effective means of lowering the oxidising potential (ORP or REDOX POTENTIAL) of the chlorinated water. and although the ONLY way to neutralise the stuff is with pure melamine powder, it is lethal if handled incorrectly, so is not available in the Eu!
The term "chlorine lock" (when stabiliser actually stops the chlorine from working) is when the ORP has dropped to close to zero. the chlorine WILL still work, but will take approximately 18 minutes, to do what it should be doing in 1/8th or a second! leaving a reagent test-kit with a tested (but clear) sample will eventually turn it yellow after this length of time...
it is however possible to raise the ORP back up by other means... but water changes works out cheaper in the long run!

If you work with 200g tablets, about 40g of each tablet would be pure Cyanuric acid. That means, on a 40 tonne (8m x 4m) pool, every tablet you add, puts the Cyanuric level up by 1PPM!
As you NEED a level of about 40PPM to start with (or the chlorine burns off in sunlight) the normal way, is to stick a good few kilos of DiChlor in to start the pool off, as there's approximately twice as much Cyanuric Acid per kilo
Put simply, Once your pool is holding chlorine, then the level is right... start counting tablets, and at the end of the summer, decide how much water you need to change, to reduce that level down to where it was...
eg 40ppm + 40 tablets, = 80ppm. change half the water, back down to 40ppm

However... many pools run smoothly with levels far in excess of 40ppm, so...

lets say it's ok running with 80ppm...
80ppm + 40 tablets = 120ppm, change 1/3 of the water, back down to 80ppm

as a rough guide, 3cm = 1 tonne, so top to bottom on the skimmer = 12cm = 4 tonne = 10%

What we do, is make an assessment of how many 10% water changes will get us back to the original level, and aim to do those over the winter, hopefully using rain.
never look at a storm as "free top up"... it's a "free water change"!

the golden hi-lux,

Thank you very much; very useful.

My pool is indeed 4x8m. Noting your 1ppm per tablet, that means each year, by using 2 large tablets per week (1 per skimmer), I would be upping the concentration by about 100ppm/year. Since I'd use less over winter, lets call that 80ppm/year. I have changed only a little of the water, by backwashing. So, after three years of using these multitabs, it is not surprising my CYA level is over 200ppm. So that makes sense; progress in understanding and proving pool chemistry is very welcome.

Also, if I was starting with fresh water, that means my CYA level would be high in just a year. If I was aiming for 40ppm, I'd have to dilute by half - change half the water, and do that every year.
(Of course the 50% works only if you drain 50% then top it up. If you were to drain, say 25% then top-it up, you'd need to do that [u]more than twice[/u] because in effect subsequent drainings would be throwing away some of the fresh water you'd added in previous toppings-up.)
How many people do that?

It looks like my options are:
A. Change half the pool water a year, and do that by:
- tanker water (with associated risks/precautions)
- garden hose (with associated issues)
- harvesting rain water (I'd need about 75cm precipitation directly into the pool if it was half-emptied first, much more if incrementally draining and adding; or less than 75cm if I created a rain water harvesting and filtering system)
- a combination of those
B. Change tactics and use less stabilizer but more chlorine.
C. Change to use alternative sanitizing technology, such as copper/silver/zinc ionization with UV, maybe with additional ozonation to break down fats and oils. (I'm not keen on electrolytic chlorination because of the Euro500+ cost of replacing the cell every couple of years; Cu/Ag/Zn electrodes are cheaper).

Does that sound right?

Yes, that's pretty much right...
remember all the "electronic" methods only produce sanitizing chemicals when the pump is running, and have a maximum output... for instance a 40gph salt-water chlorination system produces a maximum of 40 grammes of chlorine GAS ever hour; the concentration of that chlorine gas is only about a tenth of that of tablets, and you're predicting a useage of 2 tabs a week (400g) so to get that level, you need to run your pump for about 100 hours a week; about 14 hours a day... probably far more than you are presently doing?
Those water-changes are looking cheaper again aren't they?

That's interesting; always good to have some calculations to back things up; thanks.

As I said, I'm not thinking of using a chlorinator. But while you mention that...
You say it produces chlorine gas (presumably you mean chlorine atoms in the form of ions). But that still ends up as hypochlorous acid in the water, yes?

As for running costs (for any electric system), I am looking at installing a photovoltaic system, without batteries and inverter, driving a DC pump. That would run whenever there is sufficient insolation. That has the advantage that it runs quickest and longest in midsummer - when it is most needed.

I am aware that UV systems and ozonation systems have no residual sanitizing effect.
(I like the idea of UV because it can kill Guardia, Cryptosporidium, Polio virus, Ecoli and Coliform - which are not killed by chlorine (paraphrasing).
Lots of potentially good info here - http://www.lenntech.com/systems/uv/swim ... z32i3Courg)

The manufacturers of copper/silver/zinc ionization systems, however, seem to indicate that there is some residual effect.
(I could believe there might be some residual effect, which from a marketing viewpoint, the manufacturers could be over-emphasizing.)
For example, ECOsmarte states:
“The residual [effect] is recognized by the National Sanitation Foundation (NSF) and the U.S. Environmental Protection Agency.
... each ECOsmarte oxidizer is more powerful than sodium hypochlorite, the dominant form of chlorine.
... The only reason to add chemicals to your pool will be to control pH.”
[http://www.ecosmartepool.com/poolwatertreatment.html]
Alligator seems a bit more realistic, stating:
"The Aligator system uses copper and silver ionisation techniques to purify your swimming pool water, drastically reducing the amount of chlorine you need to maintain your pool. This is good news for swimmers who are allergic to chlorine."
[http://www.aligator.com/faq.php]
But then it also states:
"creating a residual disinfectant/algaecide throughout the whole pool
... The system is not affected by heat or light and provides much longer residuals than chemical or UV treatment."
[http://www.aligator.com/how-it-works.php]
What's your take on these claims, and on residual effects of metal ionization in general?

Hi Mike.
Regarding Cyanuric Acid levels this is a problem in many Swimming Pools,The correct amount should be about 40 PPM now more than 50 most test strips do give these readings. There is a lot of Cyanuric acid used in less expensive Chlorine making levels high over a short period of time. We all know that this product is very corrosive when levels are high also other chemicals will not work as they should do, plus health issues. How to overcome this problem weekly Backwashing when levels get to 50 Start using Shock Granules Hypochlorite, as Cyanuric will always be in your water. I have a pool also in Cyprus with no troubles aligator low Chlorine
Regards Steve.

Hi Stephen,

Thanks for your input.
My cyanuric acid level is over 300ppm. I know I need to do something about it, and an Aligator is one of the options I am considering once I've brought the CYA concentration down.