Chemicals In New Pool

[greggb]

Hi all. We recently acquired a 5000 gallon above-ground pool. We filled it up a few days ago and today I'm trying to get a handle on the chemicals. I've been googling a lot and feel like I have a pretty good idea of how to go about things, but I was hoping to get some advice from some real-life people.

I keep aquariums, and have some understanding of water chemistry... things like pH, buffers, etc. From what I'm reading I should be going for a pH of 7.2 or so, and a chlorine level of 2 ppm.

In all the reading I've done I haven't heard much mention of buffers or the role they play in pH. Our water is hard and contains a natural buffer, so I'm anticipating that the pH Minus I'm adding won't have much effect on pH until the buffer has been broken down. I was wondering if there are any general rules regarding buffers in typical hard water? Or is the best plan to just add x amount daily until you get your desired pH?

Our pool came with a test kit for pH and chlorine. I have aquarium test kits for pH and chlorine too... I'll probably use both and see how they compare. The kit that came with the pool mentioned that chlorine in the water would have a serious effect on the pH reading. Is that generally the case with pH tests, and if so, how can you get an accurate reading when there's pretty much always going to be chlorine in the water?

I added some chlorine to the pool this morning. I've noticed it's not dissolving very quickly. I thought that might be related the alkalinity of the water (out of the tap pH=7.8), so I added some pH Minus too. As soon as the chlorine dissolves I'm going to run some tests and see where that puts me. And of course I have the kids asking me when they can get in the pool every 5 minutes. I'm really nervous about letting them get in if there's any chance that there's undissolved chemicals in the water. Is there a basic rule as to how long you should wait before allowing people in the pool after adding chemicals?

Any advice would be greatly appreciated. Thanks in advance!

Gregg

[chem geek]

Gregg,

First of all, please get yourself a good test kit. The one you have isn't sufficient for pool water testing. The best is the Taylor K-2006 kit you can get at a good online price here or the TF-100 you can get here with the latter kit having more volume of reagents so is comparably priced per test. You can compare these kits in this post. I have both and prefer the pH test in the K-2006 but like the reagent sizes (especially extra CYA reagent) in the TF-100.

As for buffers, hard water usually, but not always, has high Total Alkalinity (TA) which is the buffering you refer to. When you get the good test kit you will be able to explicitly measure the Calcium Hardness (CH) and Total Alkalinity (TA) as well as Cyanuric Acid (CYA), pH, Free Chlorine (FC) and Combined Chlorine (CC) with very good accuracy. The tests are more expensive because they use a FAS-DPD chlorine test that doesn't bleach out at high chlorine levels, can measure up to 50 ppm FC (useful when shocking a pool), and can measure with a resolution and accuracy of 0.2 ppm if needed (using a 25 ml sample size; with a 10 ml sample size the resolution/accuracy is 0.5 ppm).

Acid is the only way to lower TA (other than water replacement with water lower in TA). There is a procedure combining such acid addition with aeration at low pH that speeds up the process. It is described in the Pool School which has a lot of other helpful information for how to maintain your pool.

The pH test in the kits I recommended have some chlorine neutralizers in them that let you read the pH reasonably well up to around 10 ppm FC. For higher chlorine levels, such as when shocking, the pH test can read falsely high so you want to get your pH in line before shocking -- usually having the pH lower to start with, say 7.2, since shocking with a hypochorite source raises the pH until the chlorine level comes back down.

I would not say that a pH of 7.2 is ideal. 7.5 is the closest to the average pH of human tears and is also reasonably stable at recommended TA levels not above 80 ppm when using hypochlorite sources of chlorine.

It sounds like you are using a source of chlorine that is adding something else to the water. The following are chemical rules of fact that are independent of concentration of product or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So even with a low 1 ppm FC per day chlorine usage, continued use of Trichlor tabs/pucks will increase CYA by over 100 ppm in 6 months if there is no water dilution.

The active chlorine (hypochlorous acid) level that is responsible for disinfection, prevention of algae, and oxidation of bather waste is proportional to the FC/CYA ratio so as the CYA level climbs the chlorine becomes less effective unless the FC is also proportionately raised. In a manually dosed pool, having a minimum FC that is 7.5% of the CYA level will prevent algae growth. In an SWG pool, it's around an FC that is 5% of the CYA level.

I don't know what chlorine you were adding that is slow to dissolve -- sounds like it might be Cal-Hypo. You should probably be using chlorinating liquid or bleach instead or perhaps use Dichlor to start with until your CYA level is high enough or you can add pure CYA instead (either granular/flakes that are slow to dissolve or liquid CYA called Instant Pool Water Conditioner that costs more but mixes instantly).

Since your pool is smaller, you could use a simpler method and not worry so much about some of the above details and just dump your water after each season if its short. There's an article in the Pool School for such seasonal/temporary pools.

Richard

[greggb]

Thanks for the great reply Richard!

It seems like a tremendous amount of trouble I'd have to go through to do things perfectly. I can't imagine the average person who gets one of these pools at Wal-Mart (or a yardsale, like where we got ours) going to all of this trouble or being willing to learn so much about this. I could see all the trouble if it were permanent, but like you said, it's just going to be up for the summer. After that we will definitely dump it.

I'll check out the article you mentioned. Would it be advisable then to just monitor the chlorine throughout the summer and add some as necessary?

Just out of curiousity, could I use an aquarium chlorine neutralizer in a sample to neutralize the chlorine and hope to get an accurate pH reading?

Also, I got the CYA even before I'd read your post. I measured out the suggested amount for a ppm of about 20-25 and poured it in the pool. Then I read the directions completely and found out I was supposed to pour it in the skimmer, which is up and running on the pool. From the looks of things this stuff isn't going to dissolve very quickly at all. I've tried stirring it and noticed that doesn't have much of an effect. I've also noticed that some particles are suspended in the water, which tells me it's definitely not safe for people.

So now I have a bit of a mess. I guess the thing to do now is wait for it all to dissolve?

It's been cool here lately (North Idaho) and I'm guessing the water isn't much over 65 degrees. It'd be easy enough for me to check it but I haven't gotten around to doing that. But anyway, I'm thinking that might be part of the reason all the granules are taking so long to dissolve.

Thanks again for all of your help!

Gregg

[chem geek]

For a temporary pool you can dump, the easiest thing to do is to just use Dichlor for a while until the CYA build up to around 30-50 ppm (that's cumulatively adding around 33-55 ppm FC) and then switch to using bleach or chlorinating liquid. If your fill water is decent, you won't have to do anything else except monitor pH and make adjustments as needed. So it is pretty simple with a temporary pool -- in fact any vinyl pool is pretty easy as well since you don't have to worry about saturating the water with calcium carbonate to protect plaster surfaces. You can probably get away with the cheap test kit you have in this case.

However, once pool water is set, even a plaster pool is easy. I only add 12.5% chlorinating liquid to my pool twice a week plus a small amount of acid every month or two. That's it. Around $15 per month for my 16,000 gallon pool shown here and here. It doesn't get much simpler than that.

As for the CYA, yes, just wait for it to dissolve which could take up to a week. Normally you pour it into the skimmer and it gets caught in your filter slowly dissolving. Having poured it into the pool, you might consider vacuuming or scooping it up and putting it in the skimmer. Otherwise, you could brush every now and then to stir it up. It will take a while to dissolve just sitting there with no water flow. Since you've added CYA directly, you shouldn't use Dichlor and should go directly to using chlorinating liquid or bleach.

Whenever adding any concentrated chemical to the water, do so slowly over a return flow with the pump running (in the deep end, if you have one).