Newbie needs help with spa water chemistry problems

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Texas Splash said:

PH - Further Reading

www.troublefreepool.com www.troublefreepool.com
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This bit about testing pH when FC levels are above 10 (a situation I faced yesterday) is gold:
A better way to test pH in high FC water (below 20ppm) is to mix a 1:1 solution of pool water with DISTILLED water. Then test pH. Doing that will cut the FC down by half but have almost no effect on pH (due to the much higher alkalinity of pool water compared to distilled water).[4]
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Thanks again!
 
Am working to get my pH and TA dialed in after a refill and, after several rounds of MA and testing, I have them down to 7.4 and 60. Want to get TA down to 50 but, now that I'm so close, I'm unsure how to avoid "overshooting" the reduction using MA via the Pool Math app recommendations. When I go to the TA screen and enter 60 in Current TA and 50 in Target TA, it just says "To lower TA you reduce pH to 7.0-7.2 with acid then aerate to increase pH." But this doesn't tell me what my TA will be if, for example, I decrease pH to 7.0. I'm trying to avoid the yo-yo stuff of adding MA, adding baking soda, adding MA, etc. It seems like this should be a simple calculation, so I'm guessing I'm missing something in the app. Thanks!
 
OK, here's a quick update on things for anyone interested:
  • Completed the Aww-some purge (2 rounds) yesterday--lots of brown foamy gunk but actually less than I expected based on some videos I'd seen when preparing. Drained, wiped down with 50% Clorox solution and re-filled. Calibrated flow rate for 2 hoses at about 16.5 seconds/gallon (next time I fill, I'll get a multi-gallon container to help make this a bit more precise), which resulted in a total fill estimate of about 420 gallons for my 525 gallon spa (filled to bottom of highest pillow).
  • Initial testing after fill: >8.0 pH (Taylor K-2006 only reads up to 8.0 but my estimate based on later MA additions and pH reductions is that it was around 8.5); 80 TA; 80 CH; 0.0 FC
  • Added di-chlor, Acid Magic and Calcium Chloride Diydrate and re-tested: >8.0 pH (ditto; guessing 8.4); 70 TA; 10.5 FC; 9 implied CYA (based on adding 10.5 ppm di-chlor); went to bed as it was dark and very late (long story)
  • Tested this morning (12 hrs later): >8.0 pH (ditto; guessing 8.4); 70 TA; 120 CH; 8.5 FC (water temp only 70 overnight). Increased set temp to 100.
  • Added Acid Magic and re-tested: 8.0 pH; 65 TA
  • Added Acid Magic and re-tested: 7.4 pH; 60 TA
  • Added Acid Magic and re-tested: 7.0 pH; 55 TA
  • Aerated for 30 mins and re-tested: 7.6 pH; 55 TA
Goals for tomorrow:
  • Test FC to see how much it dropped over 24 hrs with no usage and temp up to 100. Add some more di-chlor to get more CYA in the water.
  • Add Borates to get to 50 ppm. I ordered some granular Boric Acid but delivery has been delayed, so I'm wondering if I should wait a few days for that or just use Gentle Spa instead. If the latter, I'm not clear on how much to use, as the bottle says nothing about ppm dosage and I don't have a test for that--would welcome any thoughts on this.
  • My Saltron Mini should arrive, so I could go ahead and add salt and get that going unless anyone would advise I wait till I've reached 30 ppm of CYA via additional di-chlor
Would appreciate any feedback/thoughts--thanks!
 
I did an Ahh-some purge (2 rounds), drain and fill on Sunday and added di-chlor to a measured FC of 10.5 that night. Water temp was at 70 when I tested roughly 12 hours later and got a 8.5 FC result. Turned heater up to normal 100 degree level and checked this morning (roughly 24 hrs later) and got a 2 FC result (along with 0.5 CC). No spa usage. There is very little CYA at this point, as I've only added 10.5 ppm FC via di-chlor, so probably around 9 CYA. My question is this--is this normal FC loss in 24 hrs with no usage and I should continue on with this batch of water? Or is this evidence that I didn't do enough Ahh-some and have a continuing demand problem? And if I do have a continuing demand problem, do you think this is something I can handle via lots of shock or is another purge/drain/fill necessary (I sure hope not). I appreciate your thoughts!
 
Some more data if anyone is still following this:
  • After my test yesterday morning, I shocked it via di-chlor with the intent to take it to 12.0 FC but I overshot a bit (Used too large of a measurement container and knew it wasn't precise, so preferred adding too much to too little; I'll use a more precise measurement next time) and tested 14.0 FC after. This puts me at 25.5 ppm di-chlor added to-date, so guessing CYA is just over 20 (still too low to measure via K-2006).
  • Tested again this morning (24 hrs from last test) and FC is now at 10.5, so it dropped only 3.5 compared to 6.5 in the prior 24-hr test (no usage either time, same water temp). Not sure what to make of this difference (note that CC remains unchanged at 0.5 this morning--same as before the shock to 14 FC). Anyone have any ideas?
  • TA remains at 50; pH has now dropped from 7.6 after aerating Monday night to 7.4 yesterday morning to 7.2 this morning (no usage and spa has been covered the entire time save for 30 mins after shocking yesterday). I'm a little surprised to see it dropping---anyone know what might be causing that?
  • My granular Boric Acid is due to arrive today, so will dose up to 50 ppm when it does
  • My Saltron Mini arrived last night--I need to buy a small extension cord for it, as the power cord doesn't quick reach to my GFCI outlet. I think I'm going to wait a couple days to set it up, as I'd like to better understand my FC loss with no usage, then with usage, before I add that to the equation.
As always, any thoughts are very welcome!
 
Vesuvius said:
Some more data if anyone is still following this
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Ha ha.

No problem over-shooting the FC a bit. As you can tell it will fall rather quickly. It's possible there are some acidic properties in your powder that is causing the pH to fall slightly. Not a big deal unless it falls below 7.2. using the tub (aeration) should increase the pH rather quickly.
 
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Texas Splash said:
Ha ha.

No problem over-shooting the FC a bit. As you can tell it will fall rather quickly. It's possible there are some acidic properties in your powder that is causing the pH to fall slightly. Not a big deal unless it falls below 7.2. using the tub (aeration) should increase the pH rather quickly.
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OK, good, that's what I figured on the FC.

OK, thanks--I'd read that di-chlor is pH neutral, so hadn't expected any declines but perhaps that's not perfectly true with my batch. Will keep an eye on it.

Regarding the difference in FC usage in the last 24 hrs vs. the previous 24 hrs, I guess the answer could be that I had some leftover nasties even after the Ahh-some purge and those were largely eliminated after I shocked to 10.5 but it took 6.5 ppm to do it (resulting in the 0.5 CC measurement after), so that the 3.5 ppm usage will be more typical for normal covered (no bathers) usage per day going forward (given that CC remained at 0.5). Does this make sense?
 
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Vesuvius said:
I'd read that di-chlor is pH neutra
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Make sure to not confuse di-chlor with cal-hypo. Di-chlor can impact pH a little, cal-hypo not so much. Feel free to use the "Effects of Adding" section in the PoolMath APP to confirm when you dose.
 
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Texas Splash said:
Make sure to not confuse di-chlor with cal-hypo. Di-chlor can impact pH a little, cal-hypo not so much. Feel free to use the "Effects of Adding" section in the PoolMath APP to confirm when you dose.
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This is super helpful--thanks. I was relying on the Taylor Water Chemistry guide that came with my K-2006 and that says di-chlor is "nearly neutral pH" but Pool Math EoA makes it clear that the pH change I saw was to be expected. Good stuff.
 
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Don't add the boric acid until you hit target ph and ta, it will make things harder for you.

I'm puzzled too on your fc drop. Did you throw the filters in the tub during the purge then rinse after? Demand is higher than it should be.

Also, I noted you consider using backing soda. I'd avoid it, less is more, practice restraint, sneak up on targets, note your changes when adding so you know what to expect.

Weigh your dichlor, compute your CYA. Chem additions math can be "reversed" to guestimate tub gallons.

On your MA additions, good job!
 
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Methuselah said:
Don't add the boric acid until you hit target ph and ta, it will make things harder for you.

I'm puzzled too on your fc drop. Did you throw the filters in the tub during the purge then rinse after? Demand is higher than it should be.

Also, I noted you consider using backing soda. I'd avoid it, less is more, practice restraint, sneak up on targets, note your changes when adding so you know what to expect.

Weigh your dichlor, compute your CYA. Chem additions math can be "reversed" to guestimate tub gallons.

On your MA additions, good job!
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Thanks! Yes, I didn't add the boric acid till I had TA at 50 and pH at 7.4, so all good there.

On the demand, I checked again this morning (23 hrs since last check) and FC was at 5.5, vs. 10.5 before. So, to recap, over 3 days with no spa usage, 24 hr FC depletion has been 7.5 ppm, 3.5 ppm and 5 ppm, respectively. On the filters, I had them in tub for 1st part of 1st round of purge (in the video I watched, the guy removed them before the purge was finished) and then I rinsed them. But that's a good point--maybe should've left in for the entire 2 rounds. I have some new filters on hand, so I could swap those in for a week or so--whatever's on the old ones (which aren't "old"--they were only installed on Jan 24) would die once they dry out, right?

On baking soda, I haven't used any yet and would only do so if TA went below 50. I was pretty careful when I brought down pH and TA not to go too low.

I appreciate all your advice on this stuff--it's been a great learning experience!
 
An update and some new questions:
  • I put in new filters, then did a 30 minute solo soak test--measured 6.0 FC before (odd that it measured only 5.5 earlier today--end points were obvious in both cases...maybe my drop sizes were slightly different?) and 5.0 FC after. 0.5 CC before and after. So, 2 FC consumption per man hour at 100 degrees water temp, 50 degrees air temp.
  • Decided to take FC to 12.0 (assuming my CYA was somewhere around 20) and Pool Math said to add 0.7 oz by weight. The Pool Math browser table says 0.7 oz di-chlor by weight is the same as 0.7 oz di-chlor by volume and volume is easier for me to manage, so I looked up teaspoon conversion amounts. Found out that 0.7 oz by volume is the same as 4.03 US teaspoons, so I added 4 tsp.
  • Re-tested in 20 mins and FC was only 9.5 (CC still at 0.5). TA and pH remain perfect at 50 and 7.4, respectively.
Questions:
  • Is 2 FC/man hour a reasonable consumption rate during use? I know this varies by a ton of factors, so not looking for "the answer", just a reasonableness test
  • Weird that 4 tsp di-chlor only increased to 9.5 rather than 12.0--is it possible that I tested too early after using the spa (I tested less than 5 mins after getting out of the water) or that I tested too soon after adding the di-chlor (I tested 20 mins after adding the chems)?
Am still not using the SWG, as I want to understand FC consumption rates before doing so. Will check FC again tomorrow to get another 24-hour no-use consumption number with the new filters in place.
 
Vesuvius said:
On baking soda, I haven't used any yet and would only do so if TA went below 50. I was pretty careful when I brought down pH and TA not to go too low.

I appreciate all your advice on this stuff--it's been a great learning experience!
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Demand seems high.

I do the final drying over an ac vent, but if they come out of the tub they get soaked in low suds detergent. Not sure I'd call that important or necessary, it's just what I do.

Above, no baking soda unless below 40... just try hard not to need to use it 😉
 
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Methuselah said:
Demand seems high.

I do the final drying over an ac vent, but if they come out of the tub they get soaked in low suds detergent. Not sure I'd call that important or necessary, it's just what I do.

Above, no baking soda unless below 40... just try hard not to need to use it 😉
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OK, will try something similar with the filters---thanks.

I understood from the pinned guide that anything less than 50 can lead to instability, but you think 40 is fine? Or is 40 not fine but you would use something other than baking soda to bring up TA (I thought baking soda was the only option to raise TA) to 50?
 
Methuselah said:
I computed ours (515 gallons, birthday suits) at 5 ppm per bather-hour. It can take some time to drop...
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OK, that makes me feel better about what I measured today, unless I tested too soon to get the full drop. How long do you wait until you test after leaving the tub?
 
Vesuvius said:
OK, will try something similar with the filters---thanks.

I understood from the pinned guide that anything less than 50 can lead to instability, but you think 40 is fine? Or is 40 not fine but you would use something other than baking soda to bring up TA (I thought baking soda was the only option to raise TA) to 50?
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pH of 7.4 and TA of 50 will be fine.

As long at pH is stable and above 7.2 the TA can be 50 or even 40. Let the pH be your guide if TA needs to be raised.
 
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