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Pool Chemistry 101: A Learning Experience


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I have been reading many posts here after getting a smack-down by chemgeek (my post incorrectly put into the spa chemistry forum) regarding phosphates and nitrates. Chemgeek, thanks for opening my eyes!

Some background: I have an 18k gallon in-ground, salt water pool built in mid 2007. My builder went belly up about 2 weeks after my pool was completed, so I've been kind of on my own with maintenance. I've been doing the maintenance myself, and on the advice of a friend started using a pool supply store for more in-depth water testing. 2- 1/2 years ago I was having an algae problem, and the pool store told me I have phosphates and particularly nitrates, and the best solution is to drain and refill. I did, and my problems went away.

Recently, I began to have similar algae problems, so had him check, and guess what? I have phosphates and nitrates! I got suspicious, and came here, and received my well-deserved smack down.

MY LESSONS:

1. FC and CYA and their relationship seem to be the key to algae control.

2. Phosphate and nitrate detection seems to be a way to sell pool chemicals.

3. Bromide additions (think that's right) are highly recommended.

4. TA can be lowered by reducing ph to 7.0, then aerating.

5. Pool pal is a great tool for android users.

What am I mis-stating? What am I missing? I'm no chemist, but want to learn as much as I can about pool chemistry.

Thank you Waterbear and Chem Geek!

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3. Bromide additions (think that's right) are highly recommended.

Where are you getting that? This isn't true unless you are talking about the 3-step bromine method for spas in which case yes, you start off with addition of sodium bromide. This does not apply to chlorinated pools or spas.

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Oh, we usually call that adding borates or boric acid. That is a completely different chemical than bromide. That's why I got confused. Yes, it's an optional addition. It's strongly recommended for spas using the Dichlor-then-bleach method because additional pH buffering is needed when one lowers the TA to 50 ppm or so, but for pools it's definitely optional and not at all required. I have it in my pool and I like it, but it's certainly not necessary.

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The rest of your lessons are correct except that lowering the TA also needs acid addition to keep the pH low during the process since aerating will raise the pH. Technically, it's the acid that lowers the TA as well as the pH while aeration raises only the pH so the net effect of the two processes (acid addition and aeration) results in a lower TA.

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The rest of your lessons are correct except that lowering the TA also needs acid addition to keep the pH low during the process since aerating will raise the pH. Technically, it's the acid that lowers the TA as well as the pH while aeration raises only the pH so the net effect of the two processes (acid addition and aeration) results in a lower TA. As for phosphates and nitrates, they are essential nutrients for algae growth, but if the FC/CYA ratio is sufficient then active chlorine will kill algae faster than it can grow regardless of nutrient level.

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I'm a new member and very much interested (and impresssed with your posted discussions I've read) in learning how to manage the chemistry of my salt water pool. I was googling in search of an adequate Algacide for my salt water pool and came across your web site. I have a Taylor Test kit that I purchased when first upgrading my pool...Approx a year ago, I decided to hire a pool man (are there really any experts) and haven't bee satisfied. The last time I recorded any chemistry levels was 6/26/2011 as:

pH 7.9,

CYAf 0.3,

FC 0.5,

TC 0.5,

CC 0.0,

TA 100,

CYA 35,

Alkc corrected 87.575

CH 240

Salt 3750 ppm

I added acid at that time and on 6/30/11 pH was 7.4.

Presently, I have an algae problems "on the horizon"

I'll get some fresh test done this evening....

Thank You

John Hogsett

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Your TA should be lowered to 70 ppm to reduce the rate of pH rise. You can optionally add 50 ppm borates (from boric acid or a combination of Borax and acid) as an additional pH buffer that also helps prevent scaling in the SWCG. Your FC target should be at least 5% of the CYA level so yours is too low. And if your pool is outdoors exposed to sunlight, your CYA should probably be closer to 80 ppm (so your FC target would be at least 4 ppm in that case).

If you are currently on the verge of getting algae, add chlorinating liquid or bleach to shock the pool -- at your CYA level raise the FC to 14 ppm and maintain it there until 1) the pool is crystal clear, 2) your overnight FC loss is <= 1 ppm and 3) your CC is <= 0.5 ppm. Run the pump 24/7 to filter the pool until it becomes clear.

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