Cant't keep chlorine despite mostly balanced chemistry

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
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My Pool: 25K gallon, 18x36 rectangle. In ground vinyl. Sand filter with auto chlorinator running on dichlor tabs
Location: Missouri

Cant't keep chlorine despite mostly balanced chemistry

Postby jobeck05 » Thu 18 Jun, 2009 12:57

I cannot seem to keep a decent chlorine level. I opened in May, superchlorinated with Cal Hypo. So far this year, I am eating through Di-Chlor tabs at a good clip, but even with a full feeder set on max (and moderate but not hot weather), I cannot keep the chlorine above 1.0 consistently. My latest test results are:
TA: 125
Adjusted TA: 95
CYA: 92
Free Chlorine 0.7
Total Chlorine 1.6
PH 7.3
Calcium 86
Phjosphates 500

Since the readings taken above, I have added a phosphate remover. But my pool is crystal clear, so I am not sure why.

At first, I thought Chlorine Lock, but my guess is I do not have a high enough CYA level, and I was told that my Chlorine level should still register high in such an event.

Typically my pool ran fine, even in hot weather, with a medium chlorinator setting and a Chlorine level around 2.0-3.0. Now I cant seem to keep the chlorine in the water.

Pool is crystal clear. We do have some slight foaming, but I think its from a slight overdose on algeacide upon pool opening.

I am considering simply a draing and refill 18 inches at a time for a week, and see if maybe some fresh water doesnt help, as I am tired of spending money on checmicals and water in my area is cheap.


Cant't keep chlorine despite mostly balanced chemistry

Postby jgfranklin » Wed 15 Jul, 2009 19:07

I have the same problem. From what I have read, our CYA levels are way too high. Mine is 95. You need a lot more minimum free chlorine in the pool to combat algae when the CYA level is this high. I too cranked up my in-line chlorinator not realizing that as the tablets dissolve more CYA is going into the pool. I switched to the chlorine granules that are 99 percent and that too adds CYA. It is a vicious cycle. I am trying to replace some of my water everyday to get the CYA down. I have already had a "green" pool and it required 11 bags of shock to get it blue again. However, even after that the next day I have 0 FC in the pool. I am switching to bleach...cheaper and does not add CYA along with some shock that also does not add CYA. What do you think about this approach? I have turned down my in-line chlorinator to control the amount of CYA going in as well. I plan to add both morning and night in order to keep the levels up to prevent algae growth. I think this year is just really going to be a wash unless I drain the pool. So my thinking is to try to limit the dollor bleeding as much as I can for the time being by using bleach and shoot for better next year with CYA around 40 to 50.
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Cant't keep chlorine despite mostly balanced chemistry

Postby chem geek » Thu 16 Jul, 2009 01:23

There are basic chemical facts that are independent of concentration of product or of pool size as follows:

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 7 ppm.

A little simple math shows that even at a low 1 ppm FC per day chlorine usage, using Trichlor as a sole source of chlorine would have the CYA rise by over 100 ppm in 6 months if there were no water dilution (splash-out, backwashing, rain dilution).

CYA significantly reduces chlorine's effeciveness. Technically, the active chlorine (hypochorous acid) concentration is proportional to the FC/CYA ratio. As the CYA level climbs, you need to raise your FC target or else algae can grow faster than chlorine can kill it. Initially, this appears as an unusual chlorine demand, but eventually leads to dull, then cloudy and then a full green algae bloom. In a manually dosed pool, you need to maintain a minimum FC of at least 7.5% of the CYA level or else algae can grow. If you want to have a lower FC/CYA ratio, then you would need to use a supplemental algaecide such as PolyQuat 60 added weekly, or use a phosphate remover including regular maintenance doses or use copper (but this can stain) or borates (we know this helps, but not sure how much).

You can learn much more about how to maintain your pool, including how to get rid of algae or shocking your pool, at the Pool School.


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