Pool Not Holding Chlorine

[safa1]

I have a 12000 gallon in ground pool in Northern California. I drained the water about two years ago. The TDS is now close to 4000 and the pool store is telling me that is the reason it is not holding chlorine. I use liquid chlorine as needed ( which is every couple of days now) as well as chlorinating tablets - I don;t use shocks or other powders. Everything else is fine and I check my water regularly. The level of stabilizer is also fine. Any other reason this is happening. I don;t want to drain the pool again so soon and have the solids go up so fast.

Thanks for the advice, in advance.

[chem geek]

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. So I doubt very much that your CYA level is "fine". If you weren't keeping your FC level at least 7.5% of the CYA level, then algae can grow faster than chlorine can kill it and at first that can appear to be unusual chlorine demand but is really nascent algae growth. The water could then become dull/cloudy as the algae becomes more visible. TDS isn't important -- it's what TDS is composed of that matters.

You should probably at least do a partial drain/refill because your CYA is likely to be high, but you also need to get your own good test kit -- the Taylor K-2006.

[safa1]

I tested the water again - the CYA is 130 and Leslie pool insists it is the sole reason for my problem - the other place that I use, equally insists that CYA of 130 is not the main problem but the total dissolved solids. Not sure what to do and whom to believe!

[chem geek]

The chlorine/CYA relationship was definitively determined in 1974. If you do not maintain an FC that is at least 7.5% of the CYA level, then algae can grow faster than chlorine can kill it. The high CYA level is the problem, especially since you didn't raise your FC proportionately as the CYA level rose. The following are some chemical facts that some of these pool stores also aren't telling you:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So if you use Trichlor tabs (or Dichlor) regularly, it doesn't take long for the CYA level to rise.

[waterbear]

High total dissolved solids per se are NOT a problem. However, if certain components of what is dissolved in the water are high they can be a problem For example, if you have high TDS but it is caused by salt (as in all pools that use a salt water chlorine generator) then the high TDS is NOT a problem. On the other hand, if what is dissolved in your pool is a high concentration of cyanurate (from stabilized chlorine usage) then ou have an over-stabilized pool. Leslie's is right and I am willing to guess that the other place is a BIoguard dealer since their corporate stance is that high stabilizer levels do not matter. However, since their parent company, Chemtura, is one of the largest manufacturers of chlorinated cyanurates this viewpoint becomes understandable since it increases their bottom line but does not help you with your pool problems!

Your Leslie dealer is correct! A CYA of 130 is way too high unless you are maintaining a free chlorine level of AT LEAST 8 ppm (up to 15 ppm) for normal chlorination levels and shocking to a minimum of 25 ppm when you need to shock. I can pretty well assume you are not!

Cyanurates are not the only component of TDS that can cause problems. High levels of calcium can also be problematic, as can very bicarbonate levels (this is your TA, btw).. However, it is better to measure these parameters individually and not really pay too much attention to TDS since the majority of the time TDS is composed of innocuous components that have no effect on your pool water chemistry. IF high TDS in and of itself is a problem then every pool using a salt water chlorine generator would not work!

There is a simple solution to your problem once you get your CYA levels back in line. STOP using chlorinated isocyanurates (trichlor and dichlor) in your pool and only use sodium hypochlorite (liquid chlorine or bleach) and you will not have the problem again! This means you will either have to dose the chlorine every day to every few days or install an automatic feed system for liquid chlorine such as a perestaltic pump.