CSI and being off on ph reading

[Jaimslaw]

At a TA of 60, my acid demands have improved (dual spillway + SWG = upward ph creep). But with CH at 350 and CYA at 70, pool math is impressing me with the need to be rather accurate with my pH readings. This because the difference between the rather narrow ph range of 7.4 and 7.8 means a rather dramatic difference in CSI. At ph of 7.8, my CSI is a fairly good -0.3, but just up the street at a seemingly good, or OK ph of 7.4, CSI jumps to a surprisingly poor -0.7.

I guess my concern is in moving my ph closer to 7.8 to get to an acceptable CSI, I may end up not knowing that my ph is actually 8.0 or worse. And for me anyways, it doesn't seem to be the case that I can ballpark my ph between 7.4 and 7.8 and be fine with that.

So I'm toying with the idea of getting a ph meter. I've read surprisingly good things about inexpensive ph meters from a lot of brewing and aquarium forums (vs somewhat of a cold shoulder to ph meters on TPC). Seems that if one can put up with what appears to be a simple calibration step, one could make good use of such a meter - not as a regular testing method but to become more familiar with, and get a more accurate feel for, what a particular ph reading looks like, color wise, on a comparator (sp?) block. You pros know these colors/ph numbers in your sleep, unlike so many of us. I often get a color that does not square with the colors on the comparator, which plays into my concerns about getting an accurate ph read (particularly if I am to hover my ph around 7.8, which I naturally tend to resist).

I am itching to use a ph meter particularly in the context of what I found to be two useful posts on ph reading;, one that describes nicely, the different colors of the various ph numbers, and another which recommends using one or two less of the red drops to help with color matching. So in a sense, I would use the ph meter to calibrate my comparator block, which hopefully will make for more accurate ph readings on my part.

I'm still on a learning curve here, but remain somewhat surprised (amazed?) at the impact ph and TA have on CSI. Will continue to read up on posts on CSI - as perhaps I am overstating the importance of getting to and maintaining a good CSI level and/or taking an accurate ph reading. And I welcome any recommendations that will help with my CSI levels.

Cheers.

 

[duraleigh]

I am overstating the importance of getting to and maintaining a good CSI level and/or taking an accurate ph reading.

There are many/most on the forum that never consult psi.

The general concensus here on the forum is that pH meters of REASONABLE pricing are simply not worth the money.

 

[Jaimslaw]

There are many/most on the forum that never consult CSI.

With my new pebble finish, I am probably doing more hand wringing than I should about CSI But I made a vow to never allow my pool chemistry to get to the point where I had a pile of "snow flakes" on the floor of my spa where the return was located, as was the case before my recent replaster, (and before and a better attitude about keeping good chem levels). CSI, being a part of the pool math calculator, naturally draws my attention (or perhaps more accurately, plays into my fears). Hope to eliminate flakes or other issues from ever happening again, so trying to be vigilant as possible as to all possible causes of that.

Some say flakes are from the SWG, but I kept mine at 30% and cleaned it regularly with never any build up seen on the plates during the cleaning. So I thought a poor CSI might be have been a contributing factor. But as I said, I'm still on a learning curve about all this and if an adverse CSI is not really something that will hurt my new baby or cause those flakes to reappear, so much the better.

 

[Crunchy]

I have pH indicator test at home and two pH meters at work, I'm also paranoid about pH (for the exact same reasons as you are) that I test every second day using all three! I recommend the meter, not sure why there is an opposition to them on here, I find it very easy to use and accurate but do have to recalibrate from time to time.

 

[duraleigh]

not sure why there is an opposition to them on here,

Who buys them at work?

 

[tim5055]

I find it very easy to use and accurate but do have to recalibrate from time to time.

There in lies the problem in my opinion. Life gets in the way. One of the first things to go in pool care is anything that takes "extra" time, like calibration of a meter.

TFP is based on making it simple for the average pool owner. You use meters at work and understand the need for calibration, many who visit this site - probably not so much.

Like you my TA wants to be low (50 in my case, 40 would actually be better) to reduce my acid demand. I don't sweat CSI, but I do know I need to keep the pH on the upper end of the scale.

 

[chem geek]

Your acid demand will be lower not only at lower TA but also at higher pH. See this chart that shows the degree of over-carbonation in a pool at various TA and pH where you can see that at lower TA and higher pH there is less over-carbonation so there will be less carbon dioxide outgassing and less pH rise as a result. The only risk of the higher pH target is metal staining if you have significant quantities of metals in the water (say, more than 0.3 ppm).

Having the pH at 7.4 would be below the Recommended Levels especially for a plaster SWG. Those levels were designed to roughly have your CSI be OK which for an SWG to reduce flaking is slightly negative. However, if you go outside the range or are on the low side for everything (except CYA), that's when looking at the CSI tells you if you are pushing too far and need to compensate elsewhere. onBalance saw plaster deterioration in plaster coupons at -0.7 and lower in his tank tests and we had a recent user at that low a CSI with low pH as well reporting increasing CH in his pool that could have partly been from dissolving of his plaster over months but was not physically noticeable (but over years it could be a problem -- see this post). A CSI of -0.7 has 1/5th the amount of calcium or carbonate (or their product) compared to full saturation. Also, for deterioration of plaster, a lower pH accelerates that process (when the CSI is negative). So for all those reasons, you should target the higher pH of 7.8 you describe. I'm not sure why you have trouble distinguishing between 7.8 and 8.0 (or 8.2) since the color gets more purple as you get higher in pH.

If you do decide to go down to 7.4, then if you want to protect your pool's finish you should have other parameters be higher and since you don't want faster carbon dioxide outgassing that means you don't want the TA higher so that leaves raising the CH (assuming temperature is where you want it). However, as I noted, a lower pH will have a faster pH rise from carbon dioxide outgassing so it would be better to instead target the higher pH.

 

[BuckeyeChris]

I'd adjust your CH so that a pH of 7.7 gives you a CSI of 0. then you are ok from 7.4 to 8.0. like chem geek referenced at the end. your pH will rise faster the lower your pH starts out, so you'll go from 7.4 to 7.6 faster than from 7.6 to 7.8.

 

[Jaimslaw]

I'd adjust your CH so that a pH of 7.7 gives you a CSI of 0. then you are ok from 7.4 to 8.0. like chem geek referenced at the end. your pH will rise faster the lower your pH starts out, so you'll go from 7.4 to 7.6 faster than from 7.6 to 7.8.

I played around in the past with the pool math calculator and actually used that to up my CH from new fill water of below 300 to 350. But I believe your suggestion would require raising my Ch from 350 to 700, correct?

Here in San Diego, tap water is 254 TOTAL hardness, which I understand is not the same as CH levels; I believe a Total Hardness level includes magnesium levels (14%???). In any event, should I not be weary of that high a CH level? On the other hand, I have seen OP state that they have no issues with very high CH levels. I guess I just need to read up more about CH and its relationship to pool plaster issues and interaction with other pool chem levels.

BTW, anyone have a rough idea of how many years it might take for my CH to rise to above the upper recommended CH level of 450, taking into account an existing CH of 350, evaporation and refill rates for Southern California, and a 13k gal pool? Maybe some of you here in SoCAL have had issues along those line.

 

[chiefwej]

CH too low, TA low. I wish I had such problems. My fill water is very high CH and high TA. Add in very high evaporation rates and a SWG and there is no way of keeping the pH from constantly rising and needing large amounts of acid. My CH will be well over 1,000 in a season or two. I can lower the TA, but with very high evaporation and high TA in fill water, it comes right back up. I have to closely monitor my CSI to hit the balance between scale and plaster damage. I shoot for -.01 and -.3

Your problems are the mirror image of mine. You have three factors that play into CSI, over which you have control, I only have one. You can raise CH, adjust TA, and adjust pH. Short of draining my pool, I can only adjust pH.

 

[Jaimslaw]

Your acid demand will be lower not only at lower TA but also at higher pH. See this chart that shows the degree of over-carbonation in a pool at various TA and pH where you can see that at lower TA and higher pH there is less over-carbonation so there will be less carbon dioxide outgassing and less pH rise as a result. The only risk of the higher pH target is metal staining if you have significant quantities of metals in the water (say, more than 0.3 ppm).

Having the pH at 7.4 would be below the Recommended Levels especially for a plaster SWG. Those levels were designed to roughly have your CSI be OK which for an SWG to reduce flaking is slightly negative. However, if you go outside the range or are on the low side for everything (except CYA), that's when looking at the CSI tells you if you are pushing too far and need to compensate elsewhere. onBalance saw plaster deterioration in plaster coupons at -0.7 and lower in his tank tests and we had a recent user at that low a CSI with low pH as well reporting increasing CH in his pool that could have partly been from dissolving of his plaster over months but was not noticeable (but over years it could be a problem -- see this post). A CSI of -0.7 has 1/5th the amount of calcium or carbonate (or their product) compared to full saturation. Also, for deterioration of plaster, a lower pH accelerates that process (when the CSI is negative). So for all those reasons, you should target the higher pH of 7.8 you describe. I'm not sure why you have trouble distinguishing between 7.8 and 8.0 (or 8.2) since the color gets more purple as you get higher in pH.

If you do decide to go down to 7.4, then if you want to protect your pool's finish you should have other parameters be higher and since you don't want faster carbon dioxide outgassing that means you don't want the TA higher so that leaves raising the CH (assuming temperature is where you want it). However, as I noted, a lower pH will have a faster pH rise from carbon dioxide outgassing so it would be better to instead target the higher pH.

I appreciate your input, particularly in respect to the higher ph levels and the CSI explanation. And the outgassing rate at the lower PH was informative as much as it was instructive about managing my SWG ph creep. Per usual, I will spend more time to read your post so as to mine all of the nuggets of information that typically are found in your posts.

Regarding your query as to why I would have trouble distinguishing between 7.8 and 8.0 (or 8.2), there are quite a few of us that do have eye issues that makes an ability to discern gradiants of one color more difficult than most - this especially being the case with the color purple (red is also problematic with some of us). This was really the whole point of my post referring to using a PH meter - to allow one to get more comfortable with ph readings using the drops vs lingering doubts about the ph reading - again as a means of a helpful supplement to the TFP method. With so many of us, its an element of our nature to want to be as precise as reasonably possible. Why this induces push back will remain a mystery to me.

I guess PH meters will continue to be a taboo subject; this notwithstanding that most every post I have read from those mentioning the use of a PH meter have never remotely advocated using the meter in place of drops; nor would such posts even tacitly induce anyone on this forum to abandon the standard method of PH testing in place of a PH meter. On the other hand there is a neat geek factor involved that requires very little expense and time that many of us warm up to. Just our nature.

 

[Jaimslaw]

CH too low, TA low. I wish I had such problems. My fill water is very high CH and high TA. Add in very high evaporation rates and a SWG and there is no way of keeping the pH from constantly rising and needing large amounts of acid. My CH will be well over 1,000 in a season or two. I can lower the TA, but with very high evaporation and high TA in fill water, it comes right back up. I have to closely monitor my CSI to hit the balance between scale and plaster damage. I shoot for -.01 and -.3

Your problems are the mirror image of mine. You have three factors that play into CSI, over which you have control, I only have one. You can raise CH, adjust TA, and adjust pH. Short of draining my pool, I can only adjust pH.

Bummer to read about your triad of chem issues that you have had thrust upon you via your water supplier. Those are crazy high CH levels. My assumption is that you have not experienced any scale or plaster damage issues. Would be curious to know if you have had such issues and if so, how they manifested.

 

[Jaimslaw]

Like you my TA wants to be low (50 in my case, 40 would actually be better) to reduce my acid demand. I don't sweat CSI, but I do know I need to keep the pH on the upper end of the scale.

For some reason, I have resisted the higher ph levels. Maybe it was a sub-conscious aversion or some primodial negative reaction to the color it gets a the higher PH level. But now firmly on the right PH path and won't sweat (too much) the CSI number. (Come to think of it, I don't think I even know what plaster etching looks like - and/or what it would look like as to a pebble finish).

I'll be dialing back my Stenner Acid feed (which BTW was a godsend re my SWG ph creep). Thanks.

The only question remaining is my prior experience with flakes. I thought my prior flaking was due to a high PH issue, as my lazy days in the past promoted longer periods of high PH (ie being able to add acid on weekends only). But perhaps flaking occurred when I would add too much acid to adjust downward the PH, such that for three days after, and prior to PH levels getting back to high, the low ph was generating those flakes.

 

[Crunchy]

Who buys them at work?

Quite right, the fact I have access to them at work is irrelevant, to re-phrase then:

I Use both the indicator test and pH meters, I find the pH meters very easy to use and accurate to two decimal places, if cost and the extra time required to calibrate them from time to time is not an issue for you, then I would recommend purchasing one.

 

[chem geek]

To get -0.7 CSI in PoolMath with pH 7.4, TA 60, CYA 70 and an assumed salt level of 3000, the temp has to be around 64ºF. Is that what you have been using? I've been assuming 0 ppm Borates. I think BuckeyeChris neglected to put in the 3000 ppm for salt and used a higher temperature in the high 80s since only then can I have a pH of 7.7 get to a CSI near 0.

As for pH meters, the better more expensive ones are fine to use if you maintain them. That's not a recommendation for most people who can use the phenol red test reasonably well but for those who have trouble reading the pH test certainly a meter is an option. Another option is a colorimeter that reads the phenol red test such as found in the ColorQ -- at least for pH it tends to do OK.

As for flakes, those would not come from low pH. More likely your other parameters such as TA were higher then they are now. Remember that it is the combination of water parameters -- those determining the CSI -- that determine whether you will get flaking from the SWCG. One thing you can consider is to add 50 ppm borates (such as from boric acid) since that roughly cuts in half the amount of pH rise in the SWCG so usually significantly cuts down flaking.

 

[Crunchy]

Great, thanks for the tip on adding Borates to assisit with flaking...

 

[Jaimslaw]

To get -0.7 CSI in PoolMath with pH 7.4, TA 60, CYA 70 and an assumed salt level of 3000, the temp has to be around 64ºF. Is that what you have been using?

Correct (Salt at 3200).

I've been assuming 0 ppm Borates. I think BuckeyeChris neglected to put in the 3000 ppm for salt and used a higher temperature in the high 80s since only then can I have a pH of 7.7 get to a CSI near 0.

Correct again. 0 Borates. And yes, he probably had a temp in the 80s as it would require a huge (700) CH level to at my temp of 64.

As for pH meters, the better more expensive ones are fine to use if you maintain them.

Actually, the $19 ones do just fine, though they obviously won't last as long as expensive meters, which can be expected at that low of a price point. The reliability is assured via calibration, which is required more often for the lower end models. And contrary to popular belief on this forum (vs brewing and aquarium forums where accurate PH is far more critical), calibration is a simple exercise: a two minute endeavor that involves no subject interpretation: simply pour a few ounces of certified ph solution ($8 on Amazon) into an unused plastic cup, place the meter into it, and turn a small screw to adjust the reading of the meter to the PH calibration solution. For some reason, this simple calibration procedure with virtually no learning curve has been mischaracterized as being a cumbersome, time consuming and complicated procedure. It's not. But this will not keep some from making the same "it's not necessary - we don't recommend it" mantra when there is not even an inference that use of a PH meter is being advocated or promoted.

That's not a recommendation for most people who can use the phenol red test reasonably well but for those who have trouble reading the pH test certainly a meter is an option. Another option is a colorimeter that reads the phenol red test such as found in the ColorQ -- at least for pH it tends to do OK.

Couldn't agree more with you.

One thing you can consider is to add 50 ppm borates (such as from boric acid) since that roughly cuts in half the amount of pH rise in the SWCG so usually significantly cuts down flaking.

I have been meaning to get on that borate train. Will get on that...as soon as I finish ordering that $19 ph meter

 

[BuckeyeChris]

yes, salt also helps, he has a swg so I assumed he was already at least 3000. For me, like chief, my Ch is already around 800. Easier to keep the TA low and the pH around 7.8. You're right though, closer to 7.6 in the winter when the water is 60 degrees.