Infinity pool! Carbon outgassing! TA?! pH?!

Hello,

I came across your website while searching the internet for solutions to an ongoing problem with an infinity pool. I've been working with this pool for about 1 year, and I'm still learning. I'll start with the stats.

The pool is 21,575 gallons, plaster, has an Infinity edge spilling over two sides, and is running into water balance issues that you are likely anticipating.

We have an automated Ecolab chem feeder, using Accutab hypochlorite pucks and muriatic acid diluted by half. The feeder is calibrated to maintain a pH of 7.4 and an ORP equivalent of 2-4 ppm chlorine. My support from Ecolab has been limited and I've had to learn most of what I know on my own, reading Taylor literature from my water test kit and online discussions. My limited working knowledge of pool care has already surpassed that of my supposed professional support.

The problem:

Unless I keep the TA down at 40-50 ppm, I can not keep the water balanced. Any time I add baking soda to raise the TA, my pH skyrockets. Running the pool with alkalinity this low for several months caused copper to precipitate and stain the corners, which we were able to remove easily in with 32 oz. of Ecolab Conquest Stain Remover (Hydroxyethylidene-1, 1-Diphosphonic Acid says the label) so I am confident the stains were not algae, the stain remover worked on the first go and between the chlorinator and a UV sanitizing system our water stays free of bugs.

A typical reading when I was running the TA at 40-50 would be

FC: 3
CC:0
pH:7.5
Calcium Hardness: 250
TA: 40

Using a S.I. cheat sheet I see that this puts my water just over the range for corrosion, which would explain the copper staining, right?

After the stains showed up, my Ecolab support said it was from the low alkalinity, which we raised to the suggested 100 ppm and the pH shot up to well over 8. Following the formula for my acid demand it suggested I add 79 oz. of muriatic acid. I added half that dose, with the intent of gradually adding the rest over a 3 day period.

Because of the aeration of the Infinity edge, however, carbon outgassing is causing a continual rise in my pH. So by the next day my acid demand according to conventional formula has actually risen. Exacerbating this is the fact that the chem-feeder will go into alarm status and stop feeding acid when the pH goes over 8 or after running for 2 hours in a 24 hour period. By the time I manage to bring my pH down to 7.4, my TA is always below 60, and generally 50 or less.

We have the infinity edge on a timer so it automatically shuts off from midnight to 7am, but the remainder of the day it is running constantly and the owners of the hotel I work for want it to run all day, the pool being a grand showpiece.

Since I began working with this pool in may of 2013 (with no prior experience, and no guidance but what I have managed to learn myself) the only solution has been to run a low TA to combat the carbon outgassing pH rise.

Using a saturation index calculator I found that if the pool were within the following parameters it should be almost perfectly balanced:

TA: 50
Calcium Harness: 250
pH: 7.7
Temp: 86 degrees


I could pull this off if I get Ecolab to come and change the parameters on our chem-feeder so it stops shooting for 7.4 pH. My question is do you think that, even though the S.I. says this will balance, is a TA of 50 and a pH of 7.7 likely to cause problems? I assume the copper precipitate we encountered was either from the copper supply lines or the heater; could low TA have induced this, even with a pH of 7.4-7.7?

Another potential solution was to raise my calcium hardness to 350 ppm and run the pH at 7.6. This would require an initial dose of 25 pounds of calcium chloride 77%. From your experience is it likely I'll be going through that much calcium chloride on a weekly basis to maintain? If it is impractical I don't want to bother ordering it from Ecolab, and it seems to me that there ought to be a way that requires less chemicals and more wits.

I apologize if I was a klutz with any terminology or info, but I need advice from someone with a real working knowledge of pools. My enemy is the Infinity edge, our 2,344 gallon hot tub has no such issues.

I appreciate any advice you can offer and look forward to learning


Ben

1. Low TA did not cause copper precip.

2. This page explains why it's not possible to maintain a 'balanced' pool that has an active 'infinity edge': http://www.poolsolutions.com/gd/lowe...p-by-step.html

Of course, you're doing by accident what that page explains how to do on purpose. Ironically, I first discovered this process on the Atlanta Hyatt Regency over 20 years ago, after installing ORP/pH controllers on both their pool and their spa. (You'll have the SAME problem on the spa, if you have pH control and active aeration.)

3. If you want a little more info, register on PoolForum.com . But I'm the only one with substantial commercial experience, and I limit my responses since the forum is focused on residential pools.

4. If you want more that that, it will take my time and your $$.

5. You are far, far more knowledgeable than most of the commercial pool staff I've encountered over the years, especially for someone associated with a hotel or motel.

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