G'Day from first time pool owner

[FrankToil]

Hello all!

I've been reading my way through your extensive website and this forum. It looks like lots of good stuff!

Some background: We bought a house with a pool about 6 months ago (in upstate New York) and have never run a pool before. It's an in-ground lined 20x40, with an estimated 30,000 gal. of water. It was a green slime-pond when we opened it up at first, but a local pool-guy started us on shocking with hypochlorite, and vacuuming/brushing. I've starting on your BBB method (I'm all for its simplicity!) but am apparently still in a bit of algae trouble or something. I've brought the pH up with Borax. We use well-water to fill the pool, since we do not have access to city water mains at our place. I bought one of the LaMotte ColorQ Pro 7 photometer-and-liquid-reagent-drop gizmos before I found your recommendations on testing kits, so these readings are from that kit.

I guess my biggest concern is that the FCl is staying down after a fair bit of granular hypocholrite and bleach, even though the CYA is about 25 or so. (I am trying to bring that up, albeit slowly with solid stabilizer from local sources. I've just ordered the Kem-Tek 024-6 from Amazon, per your recommendations. I'm also waiting on a floater for the trichlor tablets that the previous owners left behind.)

My basic questions are two: First, that kit is indicating a nonzero level of Br. Should I take that as a sign that the previous owners used to run a Bromine based system, or is it likely a "goop" side effect of some other product? I have not (knowingly) used anything with Br in it since I started dealing with this pool. If so, what's my best course of action to deal with the Br levels?

Second, I understand that the Borax and baking soda are two different chemical buffers, attempting to hold the pH at two different values. I also understand that the Borax is what brought my pH up from about 6.5 to about 7.7 or thereabouts. When would I ever need to use baking soda? (I.e., what is the purpose of a second buffering system when there's already one trying to maintain the pH levels?)

I'm a geophysicist, not a chemist, and my last chem classes were eons ago, but it's OK to get into a little bit of the chemistry (I'll catch up) but don't expect me to have any intuition for this stuff yet!

Thanks for your guidance!

[aylad]

I'll let Pooldoc handle the non-zero Br readings, except to say that if you're using an OTO block, the chlorine and bromine scales are side by side, so if you get a reading for Cl, you'll get one for Br too, even though there's no bromine in the pool. If that's the case, then ignore it. However, if your test system runs a separate test for bromine, and you're getting a level, then that's a question for Ben to handle. I'll ask him to take a look into this thread and see what he thinks.

The borax is used to raise your pH without having much of an effect on your total alk. The baking soda is used to raise your total alkalinity, which is in part your pH buffer. There are those who can (and will, if you want) go into the exact chemistry as deeply as you want to go, but the extremely oversimplified version is that the borax is changing the pH of your water, and the baking soda works on the buffering system for the pH. Does that help?

At any rate, how is the water looking now? To address the low chlorine issue, I would test for chlorine tonight after the sun goes off the pool, and then test it again in the morning before the sun hits the pool, and compare the two numbers. If you've lost more than 1 ppm of chlorine in that time, then you have something in the pool that is consuming it, so the pool needs to be shocked and held at shock level until whatever that is, is dead. If you haven't lost any chlorine overnight, then you can pretty much attribute your chlorine loss to sunlight, and increasing the CYA should help.

Welcome to the forum!

[PoolDoc]

I guess my biggest concern is that the FC is staying down after a fair bit of granular hypochlorite and bleach, even though the CYA is about 25 or so.

CYA = 25 is not high enough to prevent significant chlorine loss during a sunny day. Also, algae -- even when it's not a full 'bloom' -- introduces a substantial chlorine demand, so you need to eradicate it.

My basic questions are two: First, that kit is indicating a nonzero level of Br.

All the pool chlorine tests available are actually either free halogen tests, or else more generalized oxidizer tests. When your kit is showing a Br value, it's simply showing a chlorine value on a different scale. There's actually no deck-side method to distinguish a 1 ppm free chlorine residual from a 2.25 ppm bromine residual. (Reaction to the test reagent is molar, so the scaling factor is the molecular weight ratio -- Cl2 has a mol. wt of 70.9; Br2 has a mol. wt of 159.8.)

When would I ever need to use baking soda? (I.e., what is the purpose of a second buffering system when there's already one trying to maintain the pH levels?)

If your pH is acceptably stable, than you don't have to increase your carbonate alkalinity. However, with concrete pools, it's necessary to approach calcium carbonate saturation levels, to avoid reaching saturation by dissolving the pool walls.