Raise CH or PH / TA?

AllenA

Silver Supporter
Bronze Supporter
May 1, 2011
83
Scottsdale, AZ
Hi Everyone,
To preface: the question is how to raise CSI slightly (and further prevent it from dropping / controlling it in general) as the trend seems to be leading to a negative out of range due to unexpected (and maybe temporary) low CH in fill water.
I'll mention that I read many threads about CSI and I get it. But I fear that my low CH fill water is leading me into a bad situation.

So my pool's CH has been in the low 200's [202-215 ppm] recently. At the beginning of the season, it was around 250. I was skeptical with my test kit (usually high CH) so I took a sample today to the pool store (I know... they also tried to sell me Phosphate reducers) and got a reading that was very much in line [219 ppm]. I did buy 15 lbs of the CH Up product just in case but may return it based on your advice.

I tested my fill water's CH a week ago [135 ppm] and today [128 ppm]. It is very strange to me because I usually have CH around 400-500, in the pool at least. I never tested the fill water before but where I live is known to have high CH. I've had a couple of drains in the past few years which may have helped keep things in check and I never really paid too much attention to CH until now. Also, early March this year (refill) with an acid wash (not relevant I guess but just in case. Pool is 9 years old now).

Since the beginning of the season, I've been testing almost every 2-3 days max and my PH has been in the range of 7.5-7.8 and my TA needed a bit of a drop and I got it [123->89]. So I've been watching the CSI in the past few days drop to -0.4 and I am worried about it dropping even further. The reason the CSI dropped is due to the TA drop and because the PH decreased over the past few days to 7.5.

So my big dilemma is: given that my fill water usually has high CH, should I risk raising it manually (CH Up)? What are your experiences with city water CH fluctuations? My alternative is to let PH / TA rise to keep the CSI closer to -0.1 (SWG...). I can also raise each a bit, say 50 ppm for CH and keep PH at 7.8 and TA at 120? But using the app's calculations, it seems that keeping the CH higher will keep the CSI more constant with a wider range of PH. I also just bought enough Borax today to raise it from 30 to 50 which I'm guessing you will tell me to do first?

So my numbers for CSI yesterday (which scared me) were (in order):
PH: 7.5
TA: 87
CH: 214
CYA: 71
Temp: 93
Salt: 3600
Bor: 30
CSI -> -0.40

Fill water:
FC: 0.60
TC: 0.79 (I want to also ask about TC/FC in fill [drinking water!] but let's keep it for later...)
PH: 7.9
TA: 148
CH: 128
CYA: 10

Today's pool reading:
FC: 6.66
TC: 6.75 (also something else I want to ask about but also later...)
PH: 7.6
TA: 89
CH: 205 [pool store 214]
CYA: 69
Temp: 94
Salt: 3600
CSI: -0.29

The pool is uncovered and 90% sun all day. Nothing much falling into it.

Thanks all in advance!
Allen
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,998
Franklin, NC
Understand, you are testing with a ColorQ and we look at those results with a skeptical eye....

I'd be happier to see results from a TF100 or K2006 before I recommended drastic changes.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,623
Laughlin, NV
I would be very skeptical of the CH test from the ColorQ. It has been shown the results can be inaccurate.

With your fill water CH and the level of evaporation you have your CH should be rising. Not as quick as mine, but still rising. I would not add any calcium products until you get a more accurate reading of your pool water CH.
 
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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,623
Laughlin, NV
Also, let your pH ride at 7.8 or 8. That will not suppress your TA as much as your fill water is adding that too.
That will increase your CSI, until you can confirm your CH levels.
 
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AllenA

Silver Supporter
Bronze Supporter
May 1, 2011
83
Scottsdale, AZ
Hi Both,
You are right. I should get the recommended test kit. I got misguided earlier this year by the TA test which ended up being replaced by a new reagent (hopefully more accurate). I need to let this one go or rather have both like some others here. I'll get on that today and will also raise PH in small increments to maybe 7.9 and hold it there.

In the meantime, do we have a formula to calculate the amount of CH in the water given daily fill water CH vs. evaporation? That could be useful to foresee even with errors of margin. My math is rusty and I've been trying to figure out the formula but have not been successful so far this morning. I also can't find threads that discussed such a formula. It would be interesting to know how long would it take for my pool's CH to reach a certain undesirable rate and make preventative smaller drains earlier to keep it in check.
Allen
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,623
Laughlin, NV
Say your pool is 15000 gallons with a CH of 250.
You evaporate 15000 gallons (over 12 months or so).
You add 15000 gallons of 250 ppm CH water to replace the evaporated water over that period.

15000 x 250 + 15000 x 250 all divided by 15000. Your resulting CH would be 500 ppm.

In my pool, 6000 gallons. I start with a fresh fill of 250 ppm CH water. In about 16 months or so, my CH is 750 ppm. So I have replaced my water twice (12000 gallons) in those 16 months, with the 250 ppm CH water.

I am planning to install a water softener this fall just for my pool.

You can get the pan evaporation rate for your area off the internet.
 

AllenA

Silver Supporter
Bronze Supporter
May 1, 2011
83
Scottsdale, AZ
Hey Marty,
Thanks for that. I was going off track in my mind and you dimmed it down for me and it makes sense. Seems my area's evaporation rates would render my pool to lose about 25k per year. So it seems to be about the same as for you, once per 8 months.

So you haven't tried to control it by backwashing more frequently? What did you do in the past to bring it back down? I figure that if you drain a higher amount once it reaches higher levels or smaller amounts more frequently, the cost should be the same in terms of chemical loss (CYA, BOR, SALT) or am I missing something once again? The difference would be that a major drain would also cost for new water but smaller drains may not reach the threshold to charge more.

Now, I have another question and it would be great if @JoyfulNoise can chime in if possible. I have an electronic descaler. And Matt, I know your opinion on the products and have also followed your shared links but I'm not sure that I noticed the answer to my question which is: does it affect testing at all in any of the known test kits?
Without reading all the above: my fill water tested at ~130 ppm with the ColorQ but should be around 275-300 as per the city. (I know the CH test is not very accurate to begin with). But, could this descaling skew the numbers even further in any way with such a test?
This was not purchased btw for the pool but it does feed the pool. I know calcium is not removed and I know that this "descaling" is not supposed to last for very long (few days only as per the claim) which would be required in a pool to properly keep CH down.
This is the unit:

Allen
 

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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,623
Laughlin, NV
I have a cartridge filter so no backwash.

I just do a full water exchange every 16 months or so. Due this fall. Our water is really cheap ($3 a 1000) so the salt, CYA and acid cost more than the water.

But I do plan to put in a water softener for the pool. When the CH gets high my DW complains of dry skin. Will also let me leave pH at higher levels so my SWCG does not scale. May even try borates once I do not change the water so often.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,223
Tucson, AZ
The ColorQ hardness test is known to be very faulty. It’s not even a true calcium hardness test but rather a total hardness test. So if the ColorQ is reporting a lower value than what you would expect then either the regent/indicator is bad or the photometer is not properly calibrated. Either way, a Taylor CH test is much more accurate.

As for the “electronic descaler”, since their “claim” is that the the technology simply changes the crystal structure of the calcium ion (whatever that means with respect to a solvated ion in an aqueous solution), then there should be no change in the chemical properties of the calcium ion which would mean the chemical test should be unaffected by the presence of that unit. So I really doubt that is the cause.
 

AllenA

Silver Supporter
Bronze Supporter
May 1, 2011
83
Scottsdale, AZ
Hey Marty,
Thanks again for the info. I'll try to figure out how much more frequent backwashing can help. It's a shame though as I'd be losing so much. Maybe I'll also think about a water softener. I used to have one but it broke and decided to replace it with the descaler. Anyway, we'll see...

Matt, yeah, I also knew that ColorQ measures total H rather than Calcium H but it's also strange how many report it giving lower numbers compared to the better kits. Must be that much faulty. In either case, I'll get a better CH test for now and ride it out for other tests until next year. I also noticed the idea of BOR testing based on your suggestion with the other reagents. That's a good benefit over the strips which are just horrible.
Allen
 

AllenA

Silver Supporter
Bronze Supporter
May 1, 2011
83
Scottsdale, AZ
So I got the taylor ch kit and you guys were right. Ch is much higher. I'll take a few measurements over the next few days to get an average and base my calculations on that. Thanks again. I'll also try to figure out if I can backwash more frequently to compensate on the long run.