Why so much acid?

[chem geek]

Not sure how I'll know when it's time to shock; maybe just do it the pool store way for a while based on a lapse of time; maybe every couple of weeks, or I could go by my OTO chlorine reading after 2 minute reading of FC as the test instruction state.

You should not need to shock your pool regularly. Why do you think that? Have you read the Pool School (it does not say you need to shock regularly -- SLAM is an exception)? If you properly maintain your FC/CYA level and other water chemistry parameters, you should never need to shock except possibly upon spring opening if you closer your pool over the winter.

I now know where I got the alkalinity range that I thought was appropriate (80-120), and it wasn't just from the pool store. It came from the TFP calculator provided. It's right there on the guide that comes with the calculator, so the recommended level chart sort of contradicts the recommended level shown right on the calculator.

In PoolMath in the Suggested Goal Levels section near the bottom you need to change this to "Troublefreepool.com". You probably had this set to "Traditional Pool".

Last summer at times when I'd run out of acid or just from growing weary of dawning protective gear and adding acid, I'd just let the PH go; let it drift up to where it wants to be; around 8.0; and still had no problems with the pool. My biggest worry in that situation was that I had read on TFP somewhere that the FC would not be as effective at a higher PH and thought that maybe that could lead to not enough sanitizing power, which could lead to a cloudy or green pool over time, but nothing like that's ever happened to my pool; not ever since going to the BBB method, even though I've never added that last B or any other PH increaser ever since I quit using the pucks.

We do NOT say that the chlorine effectiveness drops too much at higher pH. In fact, with CYA in the water we say the opposite that you do not need to worry about the effectiveness of chlorine as a function of pH at normal FC levels. If there were no CYA in the water, then going from a pH of 7.5 to 8.0 would have the active chlorine (hypochlorous acid) level drop by around 50% (though it's at such a high level that this isn't very relevant anyway), but with CYA in the water it only drops by 15%.

Also, we do not say that you would need to use all of the BBB and in fact that is one reason why we changed the name away from that because so many people thought you had to use all three chemicals. The BBB name came from The PoolForum as a way of indicating how grocery store items could be used instead of pool chemicals -- bleach instead of chlorinating liquid or Trichlor or Cal-Hypo, Arm & Hammer Baking Soda instead of Alkalinity Up, and 20 Mule Team Borax (or Arm & Hammer Super Washing Soda if one also wants carbonates) instead of pH Up. One generally does not need to use products for increasing pH nor TA when one is using primarily a hypochlorite source of chlorine.

So I went moonlighting on you guys to see if I could find something about my situation and viola, there it was...an article about the benefits of running a pool at high PH. Not really following this advice right now; mostly because the article doesn't go into detail about "why it's okay to do this"; and so I'm just being a little more careful about diluting my acid real well and moving PH more slowly with acid, which means whenever it reads 7.8, I hit with a few ounces of acid, instead of waiting for it to hit 8.0 and trying to move it all the way back down at once, and I don't try to move it more than a couple basis points at a time because the times I've had trouble was when I got the PH down towards the lower range or tried to move it too far, too fast. All other times, it's been very predictable and controls the level as expected; at least as is shown with my tester.

The main issue with running a pool at higher pH is the risk of metal staining. That's less of a risk in your vinyl pool and if you don't have any metal ions in your water. However, you can easily get your acid usage down by lowering the TA level (again, see the Pool School for how to do that). A lower TA target (say 60 or 70 ppm) and a higher pH target (say 7.8) will significantly lower your acid usage.

 

[gregsfc]

Thanks for the information. I'll have to go back and try to get a better or more complete understanding of some of these concepts and try to find some of the particulars that I obviously missed going through the school the first time, or maybe I forgot what I comprehended last year (which is unlikely, I usually don't forget concepts), or maybe I just misunderstood or made some erroneous assumptions trying to put it all together in my head. Whatever the case, I'll have to go back and try to get it right this time. I thought it was pretty simple, and maybe it would have been if my pool wasn't trying so hard to stay above a PH level of 7.8. I've really had an easy time keeping the FC in the target range based on CYA, and I've not really had other numbers swinging around wildly except for the few times where I over did it on acid, and my alkalinity dropped out, but even those instances, the PH may have shown as low as 7.0 the evening after the overdose, but even in those circumstances, the PH would be back up over 7.8 within two or three days.

I pretty much understood everything you've addressed except for the PH stuff, well that is after I finally got the alkalinity recommendation level cleared up, which I thought was higher. I really missed the boat on most of the PH information as you've described, because I didn't know about how CYA makes the break-up of chlorine irrelevant. I got only the first part of that and that's why I thought higher PH might lead to a lesser sanitizing effect.

I'm not that concerned about not using Borax or the BBB terminology. I got that.

As for slamming, I understand that concept too about not slamming on a regular basis as the stores suggest, it's just that it's been recommended not to use the store reports, so I wasn't sure how I'd know when to slam without a complete kit. The OTO kit states that if the chlorine shows darker after 2-minutes, that I need to slam, but it seems to always get darker, so I'm not sure about that.

So I understand the recommendation to be...to get a good kit...get my alkalinity w/i the TFP recommended levels, but to still keep the PH in the proper range, even though it's always gravitated up at 8 at all different alkalinity and CYA levels, going on 2-years now; or ever since I found this site and quit using Trichlor on a daily basis to maintain FC as the stores suggest?

 

[chem geek]

A higher TA will tend to have the pH rise faster over time. This is because TA is a measure of mostly the bicarbonate in the water and that represents how much the pool is over-carbonated. The over-carbonation has carbon dioxide outgas and when that happens the pH rises.

You need a proper test kit such as the TFTestkits TF-100 or the Taylor K-2006 (the TF-100 has more of the reagents you use the most so is more economical -- see Test Kits Compared).

As for pH rise, if you get your TA lower you should find that you use less acid. You would not try and lower your pH below 7.5. You may find it settles in closer to 7.8 which is fine. If it drifts towards 8.0 that's OK if you don't have metal ions (iron, copper) in your water and you've got a vinyl pool anyway which has less risk of metal staining. So don't worry about it too much, but I think after you get your TA to the lower end of the recommended range, you'll be able to have your pH fairly stable near 7.8.

 

[Oceansol]

This is an interesting thread. I, too, wondered about my rising PH levels, and one day it occurred to me that maybe my supply was high to begin with. I went on my city website and found a water quality report. Other than the pH, I'm not certain of the significance of some of these number (there's a lot more in the report), but I'm sure you experts on this forum can weigh in on them. I guess it shows that you may have to deal with some chemistry issues from the supply, and knowing the incoming makeup could be useful.

Here are some of the results:

pH 8.1
TA 106
hardness 242
TDS 520
Ca 57

 

[chem geek]

For fill water, it's not only the pH that is relevant but also the TA. Nevertheless, the amount of pH rise from direct replacement with the fill water isn't very much. The bigger issue is the ongoing increase in the TA coming from the fill water since higher TA will have more carbon dioxide outgassing so faster pH rise. It creeps up on you. A single week of evaporation and refill isn't a problem, but over time as the TA keeps creeping up the problem gets worse and worse unless you use enough acid to keep the TA down.

Let's say your evaporation was 1/4" per day and that your pool was an average of 4.5 feet deep. Over one week, that is a water replacement of 3.2% or in 18,000 gallons it's 583 gallons. To get 583 gallons of water from the pH of 8.1 to a pH of 7.5 would only take 0.9 fluid ounces of Muriatic Acid, but to get the TA down from 106 to 70 ppm would take 5.4 fluid ounces. So you can see that it's mostly the increase in TA that is the issue. Of course as the TA rises over time, that translates into a faster pH rise so it makes it seem like the issue is the higher pH in the fill water, but if your fill water had a pH of 7.5 you'd still see the same problem.

 

[Oceansol]

Thanks, chem geek, I've only been here a short while and I can already tell you're a "well" of information!

 

[dkjbama]

Constantly rising pH with a vinyl liner can't be blamed on curing plaster. Do you have really hard water? If TA is really high, it will drive the pH up quickly. Your area isn't noted for Limestone caves or anything, is it?

Assuming OP is on city water and not on a well, The Water Quality Reports from OP's town show that their source is surface water from Center Hill Lake. City of Cookeville, Tennessee - 2015 Consumer Confidence Report

Surface water doesn't typically have the hardness problems of well water, at least not in the South where we get plenty or rain. On the flipside, our surface water comes preloaded with fertilizer from agricultural runoff, giving out pool stores an excuse peddle stuff to remove the phosphates. I told a lady at a pool store that Trichlor was the bane of my existence. She countered that phosphates were the same thing to her and offered to test my water. I almost blew a snot on my shirt; then I paid for my pool pole and bags of salt and left.

City of Cookeville, Tennessee - Water Treatment This link shows TA of 57ppm, CH of 69ppm, and a pH of 8.24 for the city's fill water. The high pH undoubtedly comes from lime added to the water by the utility to prevent the soft water from corroding pipes due to its softness.