Alkalinity and Calcium... ?

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delirium330

delirium330

0
Dec 16, 2013
113
Sacramento, CA
New pool owner almost 1 year in and a full summer swimming season in the books, thanks for the all the advice, has been crystal clear all summer. Even got a new VS pump installed myself that has been a game changer.

My alkalinity has consistently been around 70 so over a couple of weeks (got a 60 reading one time) so I added quite a bit of baking soda (based on PoolMath) to get it up, figuring that the recommended 70-90+ range was at slight risk being on the low end. Since then I've never really seen it jump up from the baking soda additions (I diluted/mixed in a container then slowly poured in front of a return jet pushing towards the skimmer intake). Still sitting around 70... why is that, should I bother learning the finer points of alkalinity levels, or just not sweat it if sitting at 70? I can't recall what my tap water/refill water reading is, but guessing that could be impacting since we get a fair amount of evaporation in Northern CA.

Secondly, my calcium has been sitting around 225 since I've owned the pool. I should re-test my refill water, but I'm pretty sure it was relatively hard so I figured with pool refills the calcium level would slowly go up... it never has even with refilling the pool (from evaporation) all summer. The pool is Pebble-Tec and the water slightly touches some stone tile too. I read the concern with calcium is leaching from the walls... should I try and make adjustments or just not worry about it with my current levels?
 
delirium330 said:
What is CSI? Calcium? Pardon my ignorance. My pH does "okay" ... I'd say it climbs from 7.5/7.8 to 8.0/8.2 over about 3-5 days, so I usually add about 10-15oz of Muriatic Acid about every 3-5 days.
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You're fighting yourself if you're adding acid twice a week and also adding baking soda. The higher the TA the faster the pH rises, especially if you have a lot of action... like 2 waterfalls.

If you plug all your numbers into poolmath it will calculate CSI (Calcium Saturation Index). Above .6, you're likely to start growing scale. Below -.6, you'll likely start etching the plaster. I prefer to narrow the range to +/- .3. You can mess around with the targets and see what changing each parameter will do to the CSI. As long as you're close to zero on CSI, the FC is adequate for the CYA level, and the pH is in the human comfort zone, ignore the rest and enjoy the pool.
 
Richard320 said:
You're fighting yourself if you're adding acid twice a week and also adding baking soda. The higher the TA the faster the pH rises, especially if you have a lot of action... like 2 waterfalls.

If you plug all your numbers into poolmath it will calculate CSI (Calcium Saturation Index). Above .6, you're likely to start growing scale. Below -.6, you'll likely start etching the plaster. I prefer to narrow the range to +/- .3. You can mess around with the targets and see what changing each parameter will do to the CSI. As long as you're close to zero on CSI, the FC is adequate for the CYA level, and the pH is in the human comfort zone, ignore the rest and enjoy the pool.
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I only added the baking soda in that one session about a month ago, since then haven't touched it and TA is still sitting around 70 and I'm having to add acid about 1-2 times a week. I'll do a fresh test of everything tomorrow and plug into PoolMath to take a look at CSI and report back.

Side note that I rarely run the waterfalls, usually about 1-2 hours a week to give the pump some run time.
 
Alright, I got some fresh results this morning:

POOL:
FC = 4.5
pH = 7.8
TA = 60
CA = 250
CYA = 40
CC = <.5

REFILL WATER:
FC = <.5
pH = 8.2+
TA = 30
CA = 25
CYA = 0
CC = <.5

Plugging all of that into Pool Math, I get a CSI of .07 which suggests that I'm okay as is? Should I just keep monitoring pH and adding the ~10oz MA every few days?
 
Read the section in pool school about TA and acid/aeration. Adding acid lowers your pH but it also lowers your TA as well. Then, with all your waterfalls and aeration, the pH rises without any increase in TA. Your fill water TA is so low that it's not adding any alkalinity to the pool.

So in the end, you need to strike a balance between adding acid, running your spillways and waterfalls and adding alkalinity. As you've learned using PoolMath, all of these factors go into your CSI value and you seem to be doing ok with that. Regular testing is the key, just keep that up and you should be fine.

by the way, what is your method of chlorination?
 
Sounds good, thanks for the advice. The TA seems to go down VERY slowly, i.e., took the whole summer to drop from 70/80 to now 60 so I'll add some baking soda to get it up. I try and do the full suite of tests every 1-2 weeks so will keep an eye on it. I use bleach to chlorinate every morning (usually at 3-4ppm in the morning and I try to bump it up to 6-7ppm during the morning pump run time).
 
My suggestion for testing would be this -

Use a cheap OTO/pH/TA test kit (the kinds you find in Walmart) for daily water testing. This is just a "sanity check" test to make sure nothing goes out of whack.

Buy a Taylor K-2006C (~ $90 on Amazon) for once a week, full service testing. The Taylor kit is your accurate and reliable test kit. You only need to accurately test FC/CC, pH and TA once per week. CH and CYA tests can be performed monthly.

Do not go weeks without testing, that will only lead to problems.


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delirium330 said:
Will do, I'm currently using the TF-100 kit for all testing.
Click to expand...

Cool. I only suggested the cheapo testers to save you on reagents. As long as you have a weekly FC/CC reading from you DPD-FAS test and assuming nothing crazy happens, then OTO is a good way to spot check for chlorine. You can even get a cheap DPD-only colorimetry test from the pool store if you prefer pink to yellow.


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