How much is reasonable

[DanS]

Reviewing past bills from my pool service company, some of the chemical amounts used don't look right. What would be typical amounts of alkanity and calcium hardness increasers upon pool openint, assuming that they are only added on opening for a 20,000 gallon concrete pool with a salt chlorinator? Do these chemicals burn off like chlorine, or linger like cyanuric acid?

[dawndenise]

Alkalinity and calcium hardness do not burn off like chlorine. With a SWCG however, you're always fighting a rising pH. To combat the rising pH, muriatic acid is used to drop the pH which also drops your alkalinity.

A key factor is what level of alkalinity (TA) and calcium (CH) you have in your fill water and how often you need to top off your pool.

In my own case, both TA and CH were quite low in my fill water (50 TA and about 70 CH) so I needed a good amount of baking soda to raise my TA and I used calcium hypochlorite to chlorinate my water (and to raise my CH) for about 2 months until my SWCG came online.

If you know what your starting TA and CH numbers were, I'm sure the guys and gals who service pools can give you a good idea of how much is "normal" in starting up a pool.

[DanS]

Thanks for the reply. I do add muriatic acid every year to keep the ph down, so that could be a factor. I don't have readings prior to opening, but 2 weeks after chemicals were added at opening, here is what I got from the Sweetwater pool store:
Total alkilinity - 133
Adj. Total alkilinity - 103
Total Hardness - 168
Ph 7.7
Here are my readings 3 months later:
Total alkilinity - 107
Adj. Total alkilinity - 83
Total Hardness - 134
Ph 7.8
Here is what the pool company is billing for(all during pool opening):
2007 - Alk increaser 15 lbs Calc hardness increaser 15 lbs.
2006 - Alk increaser None Calc hardness increaser 30 lbs.
2005 - Alk increaser 9 lbs Calc hardness increaser 25 lbs
2004 - Alk increaser 18 lbs Calc hardness increaser 30 lbs
Does this look reasonable?

[dawndenise]

OK, Dan, here's my take on this...

First off, this is all subject to a lot of assumptions. Ideally, you'd have test results from your pool service at opening and then again about 24 hours later after the chemical additions had had time to circulate. Even just 2 weeks later, a lot of conditions could affect those results...adding water, splashout, backwashing, and even adding muriatic acid (affects TA, not CH).

But, for sake of argument, let's assume nothing happened in those 2 weeks. Approx. 5 pounds and 9 ounces of baking soda raises TA in your size pool by 20ppm. Let's round that to 5.5 pounds for the sake of our calculations. Your service added 15 pounds. That should have increased your TA by about 55ppm, so one could "assume" that your starting TA was about 78 (78 + 55 from added chemicals = 133 test result). One generally shoots for a TA of 80-120 (with some discussion on whether the higher or lower end is more beneficial to stabilizing pH).

As for calcium... if you have a vinyl pool, you don't need to worry about calcium levels. If yours is a gunite/plaster pool, you're looking for a range of about 200-400ppm.

Some calcium increaser products show a dosage of 5# in a 10,000 gallon pool to raise CH by 40ppm (my pool calculator differs a bit on this, but we'll use 40ppm because that's what's on a number of products). This translates to 10# of calcium increaser raising CH in your 20,000 gallon pool by 40ppm. Your service added 15# so that should have raised your CH by 60ppm. One can then again roughly "assume" that your starting CH was about 108 (108 + 60 from added chemicals = 168 test result). You definitely needed some calcium IF you have a gunite/plaster pool.

The experts on pool chemistry will have to weigh in here on how well-balanced your water is and if there are any other adjustments needed in my calculations...and there probably are some.:o

As a final note, you may want to give some serious thought to doing your own water testing and chemical additions. It's not that hard once you get the hang of it. A good drops-based testing kit will let you fine-tune your chemicals whenever you want with just the exact amount of what's needed. And, you'll probably pay a lot less for the chemicals you add. Just some food for thought...:)