Complicated Pool Chemisty Problem

What is floc, clarifier, stabilizer, cyanuric acid,
algaecide, brightener, dichlor, sodium hypo,
sodium bisulfate, ....??
Pool Newbie
Pool Newbie
Posts: 1
Joined: Fri 05 Aug, 2011 09:59
My Pool: SwimEx 600, Counter Current
3,200 gallons, surface area 72 s.f.
Location: Chicago

Complicated Pool Chemisty Problem

Postby rrz » Fri 05 Aug, 2011 10:19

Hi everyone,

I first want to thank everyone in the forum for the great advice. I've learned a great deal about managing the chemistry of my pool, but in the end I am really at a loss on how to handle my specific situation. The specific problem is low FCL, sometimes going down to almost zero.I am trying to find a happy medium between using my water controller (ORP based) and ozone generator to maintain the right amount of sanitizer (chlorine) – a side question is about my daughters light blond hair getting a tint of green after being in the pool. I'll lay out the basic facts, and include some of details that are part of the puzzle. I apologize in advance for all the detail, but in my situation I think that all the pieces are important to know if any of you are kind enough to provide your insight and suggestions!

My location: Chicago

Pool type: SwimEx countercurrent pool, fiberglass, with larger amount of stainless steel than normal in a pool due to large stainless steel grates in the front and back. There are 2 stainless steel grates, roughly 5 feet x 4 feet each. If you want to get a better idea of what the pool looks like here is a link with pictures --

Size: 3,200 gallons, surface area is about 72 s.f.

Enclosure -- We have the pool installed outside our home in the backyard. Because we use it year round, we have a small retractable enclosure which covers the pool. The enclosure is small, about 9 feet wide, 13 feet long, and 3 feet tall. In total, there is about 350 cubic feet of air over the pool. In the summer, the enclosure telescopes open (for a picture of a similar enclosure you can check out this link ... ge_id=1310

I include this as part of the puzzle because in the winter, the enclosure is closed 100% of the time, and while the enclosure doesn't create an air tight seal, there is no significant amount of air movement. The enclosure does a good job of keeping out rain and leaves.

I am using tri-chlor via an in-line feeder. I also have a controller from Aquasol which relies on ORP measurements to control the amount of water flowing through the chlorine feeder. The controller also manages PH and controls a second pump.

I do have a ozone generator from Del installed (the small Nano model), but as I'll get into later I've been struggling with the best way to operate it in my situation (i.e., ozone generators and ORP based controllers apparently cause reading conflicts in pools like mine that are blanket covered most of the day ... or at least that is what I have been finding out). Lately, the ozone generator has been off as I have been trying to reduce the number of variables. When it is on, it is only on when the pump and ORP generator are on. (they are all linked together with a Jandy controller so they are powered on together, but I am able to manually turn off the switch for the Del ozonator)

Other info:
We like using a blanket on top of the water mainly to reduce evaporation and keep heat in during the winter.

I have the pump set to turn on twice a day for 90 minutes (in the morning and evening), and if the pool is in use, we make sure to turn the pump is on. The water controller is linked to the pump operation, so if the pump is on, the water controller is on. One area I am thinking about is that the pump and water controller are not on enough in the summer when the pool is in use a lot. Based on my calculation based using pump specifications for flow and my calculation of head, the water in the pool should be turning over two to three times over a 90 minute period.

Here is a fairly typical reading of the chemistry (with other comments in parenthesis).. the one caveat is that I did use non-chlorine shock about a week earlier. I use a LaMotte ColorQ test kit with tablets (all tablets are good, all are years from being expired)

FCL 1.06 (it is common for my TCL reading to often be 2 to 3 times the FCL reading when the pool is in use -- especially in the summer when the kids are using it a lot. When it gets in this state I shock using non-chlorine shock)
TCL 1.74
PH 7.2
Alk 56 (it always below 100, usually below 80). I have used Sodium Bicarbonate in the past to raise the alkalinity level, and the highest it has ever been after adding Sodium Bicarbonate is around 115, and then came down by itself in a few days). It seems as though the natural alkalinity of the pool is on the lower side.
CHard 127 (usually is between 100 and 130). Highest reading ever was around 150, and it has never been below 100)
CYA -- This is a tough one to give a general reading, but with this set of readings the reading was 107 ... the highest it has ever been. Usually it is very low, around 50 or below (at least in the winter time, but during the summer it has been higher in the 70-100 range.
ORP -- The ORP reading from my water controller is typically around 400-500, with the ozone generator not turned on at all. The 400-500 reading seems to roughly correlate in my pool to a 0.5 - 1.0 FCL

Temperature - This is set at 85 degrees year round, and the pump and heater work to maintain this temperature during the two, 90 minute periods they are on each day.

Saturation index -- Usually on the negative side, for this reading it was worse than normal -1.1 .... it's usually between -0.2 and -0.5

Thank you in advance to anyone who has read through all this detail. As I mentioned upfront, I would appreciate any insight or suggestions on how best to work with my ORP water controller and the ozone generator, especially while the blanket is on. The specific problem is low FCL, sometimes going down to almost zero. My understanding is that when the ozone generator is on the lack of interaction with the air due to the blanket impacts the ORP reading … I have no idea if this is true, but in the winter, the cover is on all the time, and the enclosure is closed over the pool so there is no moving air.) I also should point out that we've had the pool for a year, and I haven't yet replaced the water.

Thank you in advance for any help! (any advice on green hair would also be appreciated)


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

Complicated Pool Chemisty Problem

Postby chem geek » Fri 05 Aug, 2011 21:11


The following are chemical facts that are independent of concentration of product or of pool size:

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.

You are using Trichlor tabs in an inline chlorinator. Even with a low 1 ppm FC per day chlorine usage, your CYA would increase by around 18 ppm PER MONTH if there were no water dilution. So the rise in your CYA level over time is not at all surprising. The higher CYA level will make the chlorine less effective. Your ORP readings are very low which may mean that your ORP controller is not properly calibrated (or sensor cleaned) or that your CYA level is higher than you think since that will lower the active chlorine level that the ORP is roughly reading.

Trichlor is also very acidic. This is why the Total Alkalinity (TA) drops over time. For every 10 ppm FC added by Trichlor, it will lower TA by 7 ppm after accounting for chlorine usage/consumption which is also acidic. So that explains why your pH and TA are both dropping over time. If you use pH Up (sodium carbonate) to raise the pH, then that will raise the TA substantially as well.

If there is any residual ozone that makes it to your ORP sensor, then it will raise the ORP level and your ORP controller will then turn down the chlorine level. That could explain why your FC level is too low. Ozone and ORP controllers often do not play well together for this reason. Also recognize that ozone reacts with chlorine so if the ozonator is on and is very powerful, then it will lower the FC level unless the bather load is high in which case it will handle that load instead of needing so much chlorine to do so. That could be the other reason your FC is too low (i.e. you shouldn't run the ozonator for too long a period of time in between pool usage). However, the fact that you register such high CC levels when you are in the pool in spite of the pump running would tend to indicate that your ozonator isn't working as it should since it should be able to keep the CC in check without having you to resort to using MPS.

As for your daughter's hair turning green, that is from copper in the water so you should have your water tested for metal ion (copper, iron) content. Perhaps you have been using an algaecide that contains copper or maybe the Trichlor pucks you have been using contain copper. If you know the brand, you can look up the MSDS or check the label.

Read the Pool School to learn more.


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