Should I "leave well enough alone"?

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
neville
Pool Newbie
Pool Newbie
Posts: 4
Joined: Wed 20 Jul, 2011 14:41
My Pool: inground, 74,000 litres
Location: Victoria BC Canada

Should I "leave well enough alone"?

Postby neville » Wed 20 Jul, 2011 15:30

Here's the stats first:

Victoria BC Canada - pool temp kept around 84F with heat pump - 74,000 litre inground pool - gunite/marcite - 30 years old - newly painted in June with Zenon Epoxy paint system - testing new fill daily - currently stats are: CYA 32ppm - FCL - 2 to 3ppm - pH 7.2 - ALY 138 - CH 62

I use 1 or 2 - 200g pucks of tichloroisocyanuric in my skimmers as base line for chlorine and supplement every 2nd day or so with about 10oz of granular HTH calcium hypochlorite (45%) in pail of water poured into skimmer. Hard to get the 65% here.

Pool water looks, smells, etc. GREAT!

Here's the questions:

1) pH at 7.2 seems a bit low (borderline) but when I attempt to raise with Borax, ALY increases into mid 140s. Seems a bit difficult to get pH up. Should I try to raise pH inspite of ALY increase or leave well enough alone? pH seems reasonabily stable. Any thoughts on where ALY should?

2)CH is low but I have continued to work on FCL, pH, and ALY for now. Figuire use of calcium hypochlorite will increase calcium. Should I add calcium chloride to pool to bring up hardness level more quickly or what?

3) If HTH is only 45% what makes up the rest of that stuff?

4)Any other suggestions that you have would be appreciated.

Thanks very much!


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

Should I "leave well enough alone"?

Postby chem geek » Wed 20 Jul, 2011 22:30

Trichlor is very acidic so should not normally be used in the skimmer. If your pump cycles on and off, then concentrated acidity gets blasted through your system which can cause problems with copper heat exchangers and pump seals.

If you want to use Trichlor, then a high TA is OK especially since your CH is low so you are not at the risk of scaling. A higher TA will help balance the acidity better via outgassing of carbon dioxide. You should use The Pool Calculator to calculate the saturation index to figure how much Calcium Chloride to add (or how much Cal-Hypo to use over time).

For every 10 ppm Free Chlorine (FC) added by Trichlor, it will also increase Cyanuric Acid (CYA) by 6 ppm. So over time your CYA will increase which reduces chlorine effectiveness and you can get algae in the pool if you don't maintain a higher FC level or use supplemental products. Read the Pool School for more info.

The rest of Cal-Hypo is mostly salt (sodium chloride) and some calcium chloride, calcium chlorate, calcium hydroxide.
neville
Pool Newbie
Pool Newbie
Posts: 4
Joined: Wed 20 Jul, 2011 14:41
My Pool: inground, 74,000 litres
Location: Victoria BC Canada

Should I "leave well enough alone"?

Postby neville » Thu 21 Jul, 2011 09:48

Thanks very much - I'll try and minimize the use of Trichlor but it is very convenient for making sure there is always going to be some Chlorine in the pool. I'll keep an eye on CYA levels and pump is always on.

Am I correct that vinyl and painted surfaces are considered the same for calculation purposes?
Do I take it that pH of 7.2 is OK and there is no need to try and get it a bit higher?
What level are you meaning when you say a "higher" TA?
Do you have any thoughts on a starting target CA given the continuing use of Cal-Hypo and the higher TA?


I calculated CSI - values are: NOW (-0.7) TARGET (0.08). I'm not sure what this actually tells me and how I get from this to "how much Cal-Hypo to use over time". I am reluctant to add large amounts (11kg) of calcium chloride given the high TA. It seems like this is a real balancing act if calcium is being added when using Cal-Hypo for disinfecting and then I add a large dose of calcium chloride. Seems like a similar problem to using Trichlor, and increasing Cyanuric Acid while reducing pH.

Thanks again!
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Should I "leave well enough alone"?

Postby chem geek » Thu 21 Jul, 2011 11:56

I don't know if a painted pool will require the water to be saturated with calcium carbonate. In theory, if the paint were completely protecting the plaster, then it probably isn't needed (i.e. it's more like having a vinyl pool), but I can't say for sure. Generally painting is not recommended and often leads to problems with peeling, cracking, chipping later on. Perhaps some PBs with painted pool experience can chime in on whether CH levels should be raised to protect painted pool surfaces or whether that is not necessary. Note that if you have exposed grout in between tile that is in the water, then that will also require calcium carbonate saturation.

A pH of 7.2 is OK though 7.5 is more usual. Nevertheless, when using Trichlor tabs, the pH will drop over time so you'll need to add pH Up (sodium carbonate -- same as Arm & Hammer Super Washing Soda; careful: NOT the laundry detergent). As for how high a TA, whatever it takes for the pH to be more stable, but I'd just leave it roughly where it is or around 150 ppm. Just note that the higher TA will limit your CH to not over-saturate and that limits how much Cal-Hypo you'll be able to use. For every 10 ppm FC added by Cal-Hypo, it also increases CH by at least 7 ppm.

I agree with your concern about not raising the CH too much given the high TA and how doing so would limit your ability to use Cal-Hypo. If the answer to the saturation question is that your pool doesn't need to be saturated, then you've got more leeway for using Cal-Hypo.

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