Chlorine won't come down

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
allencrew
Pool Newbie
Pool Newbie
Posts: 2
Joined: Tue 24 Jul, 2012 09:37
My Pool: 60,000 gallons, chlorine, sand filter

Chlorine won't come down

Postby allencrew » Tue 24 Jul, 2012 09:51

This forum and the Pool School have been immensely helpful through the past few years of pool ownership. However, I find myself with a problem that seems to be ever increasing....our chlorine levels are very high, and stay high for a long time after shocking (many days), even if we remove all other chlorine sources from the pool. It's been this way for the last 2 years, I'd say, but this year the FC levels never seem to get within the "normal range" appropriate with our CYA level.

Stats:
CYA 90-100 ppm (haven't checked this in about a month)
FC: 40 ppm (shocked last evening)
CC: 0

The problem is that the FC hasn't really gotten below 20 ppm this year, and if it does get down around that level, we show CC and shock, perpetuating the cycle. If there is CC and we don't shock right away, BAM, algae like crazy.

We have a broken chlorine feeder, and so have our 3" tablets (Trichloro-S-Triazinetrione) in the skimmers for general chlorinating. We use super shock (Calcium Hypochlorite) to shock. There have been a couple times this summer where we've had to shock twice in one week.

Any ideas? Are we using the wrong kind of chlorine, perpetually raising the CYA? We really had a hard time with algae last year, leading us to buy the Taylor kit, which has helped a great deal, but I feel we're overchlorinating (it's expensive and I'm worried it's not good for my kids' health).

Any advice appreciated. All other pool stats (pH, TA, etc.) have always been fine after adjusting at opening in the summer.


chem geek
Pool Industry Leader
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Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Chlorine won't come down

Postby chem geek » Tue 24 Jul, 2012 22:19

If the chlorine level isn't dropping in sunlight during the day, then your CYA may be very very high. You say you have the Taylor kit, but is the black dot really disappearing at the 90 ppm line or is it before the 100 line? And yes, for every 10 ppm Free Chlorine (FC) using Trichlor, it increases Cyanuric Acid (CYA) by 6 ppm. Your minimum FC would be 7.5% of the CYA level so I bet your CYA is very high and when your FC drops below the minimum then algae starts to grow.

You'd need to use chlorinating liquid or bleach as your primary chlorine source to avoid adding CYA from Trichlor or Dichlor (or CH from Cal-Hypo).
allencrew
Pool Newbie
Pool Newbie
Posts: 2
Joined: Tue 24 Jul, 2012 09:37
My Pool: 60,000 gallons, chlorine, sand filter

Chlorine won't come down

Postby allencrew » Wed 25 Jul, 2012 07:19

I'll test the CYA again today....how much pool water do I have to drain to lower the CYA level considerably? The pool is 60,000 gallons....too big in my opinion, but we didn't put it in!

Is bleach the easiest way to go? Is there a particular type of liquid chlorine that is better? My local pool store doesn't carry liquid chlorine, so I'll need to buy online. In the Swim has a powdered liquid chlorine--what about that?
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Chlorine won't come down

Postby chem geek » Thu 26 Jul, 2012 02:42

There is no such thing as "powdered liquid chlorine". You are probably talking about chlorinating granules which could be Dichlor (which adds to CYA), granular Trichlor (which also adds to CYA) or granular Cal-Hypo (which adds to CH).

Lowering CYA is done with straight water dilution so to lower it by half means replacing half the water. So with a big pool that's a real hassle. Everything is more expensive with a big pool. Though using chlorinating liquid or bleach would prevent any buildup of CYA or CH, it would take a lot for your big pool. You can read the Pool School for more info.

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