Water quality - Spanish Real Estate forum - Spanish property

John97 · 06-23-2008, 10:10 PM

I have heard talk that water can get "old". Does water ever need to be completely replaced in pools which are well maintained?
My pool is about 5 years old now, has been professionally maintained to a high standard throughout. Should I be thinking of a major replenishment?
I would be grateful for some advice.
John 97

Homefinder · 06-24-2008, 12:25 AM

Thank you John97 for a very interesting question.

The non-technical answer –

Yes, the water does get old and should be partly or completely drained periodically, otherwise sanitization is compromised.

The semi-technical answer–

Please read my post on “Chlorine for Swimming Pools” for full details.

Basically, when water falls out of the sky in the form of rain or snow it is fairly pure. As soon as it reaches the earth it starts to dissolve other matter.
In some case the presence of this other matter is temporary in others it is permanent and we call this TDS (Totally Dissolved Solids).
High TDS compromises the water’s ability to dissolve more matter e.g. soap does not lather well in seawater (which has a very high TDS).

The same thing happens with swimming pool water. After a while the TDS builds up to such a high level that the sanitizing chemicals do not dissolve so well.

Actually, if common chlorine-based chemicals are used (TriChlor or Dichclor), then long before the TDS gets high enough to consider the CYA (Cyanuric Acid) has increased to the point that the sanitizer is severely compromised.

This is easy to understand if you consider that one 200 gram TriChlor tablet provides approx. 2.4 ppm (parts per million) Cyanuric acid and only 2 ppm of Chlorine.
Furthermore, the Chlorine is consumed in the sanitization process but the CYA remains and become resident in the water.

A little CYA is good: CYA is added to the Chlorine to stabilise it i.e. to prevent it from “gassing” out of the water in strong sunlight. The optimum amount is considered to be 30 ppm to 70 ppm (between 12 to 30 TriChlor Tablets).

A lot of CYA is bad news: The absolute maximum is considered to be 150 ppm (60 tablets), after which point sanitization is only achieved by using more and more TriChlor.
Finally a point is reached when sanitization becomes impossible and the Chlorine “locks up” completely.

Allowance has to be made for water loss caused by leakage, splashing out and backwashing but most pools go “critical” sometime during the second year. After this more and more TriChlor is required and correct sanitization becomes more difficult.

The Solutions: The CYA level should be checked at least once a year and any pool chemical supplier will do this or sell a DIY test kit.
When the level reaches 150 ppm or when higher levels of Chlorine are required to keep the water sparkling clear, there are two options –

· The pool should be partly drained to reduce the CYA to a reasonable level.
· The sanitizer should be switched to Bromine, which is hardly affected by CYA.

Important Please Note: The Cyanic Acid levels are simply mentioned as being “practical”.
Chemists are aware of the risks of CYA excess and anywhere that health and safety is an important issue (such as a public or municipal pool) the levels of CYA and TDS are strictly controlled by legislation.
This obviously varies from place to place but the maximum is generally 70 ppm for CYA.

For the Highly Technical Answer -

PM the member "PoolManJohn"

Homefinder

John97 · 06-25-2008, 08:35 PM

Thanks for such a detailed reply. It seems I shall have to think about replenishing at some stage.
In an area (Moraira) where water is a scarce resource it seems wasteful just to "pull the plug" and let the water drain out. Is there some way to recycle the water for irrigation or some other useful purpose?
Are there alternative sources of new water other than the expensive option of just filling it up from the mains?
I'd be grateful for some advice.
John97

Homefinder · 06-26-2008, 05:28 AM

Quote:

It seems I shall have to think about replenishing at some stage.
In an area (Moraira) where water is a scarce resource it seems wasteful just to "pull the plug" and let the water drain out. Is there some way to recycle the water for irrigation or some other useful purpose?

Quite right, water is a scarce (and expensive) resource but it not always necessary to "pull the plug". Obviously you cannot go on for absolutely ever with the same water but then every pool needs draining periodically to re-grout, replace broken tiles etc. Therefore it makes sense to extend the life of a pool full of water until draining is absolutely necessary.

The best way to do this is to convert the pool to Bromine before things get out of hand. Most pool cleaners have the knowledge to do this. Anyhow, I shall be writing about Bromine for swimming pools as soon as I get the time.

How to tell when to convert to Bromine -

When 3 or 4 ppm of Chlorine is no longer enough to keep the water sparkling.
If the water goes "murky" and has to be shocked on a regular basis.
When the Cyanuric Acid goes over 150 or 200 ppm.

Don't leave it too late and don't try to do it in the Summer as the water takes a long time to "settle down". Best to get your pool cleaner to do a full analysis this Autumn, including Cyanuric Acid.
If he doesn't know about Bromine then suggest that he joins this forum.

Homefinder