Dealing with high calcium hardness and calcium nodules

wideload

Member
Apr 23, 2014
8
San Carlos, CA
I've got calcium nodules and general calcium "roughness" (scaling) on my plaster -- it's getting worse each year. In doing my numbers, I think I've realized my problems but would love group confirmation.

Location: southern california.

FC: 5
CC: .5
pH: 6.8 // This is normally ~7.6. I've been keeping it lower last 4 weeks hoping to eliminate some of the rough calcium
TA: 90
CH: 925 (!!!, whoops)
CYA: 35 (need to bump this)
Salt: 2,800ppm (need to bump this too)
Water temp: 80F. This varies a lot. I'll heat it up to 100F for some winter weekends. Then let it drop back to 65F for most of the month.

12,000 gallon SWG pool that is plaster (or maybe plaster/aggregate??)

Nodules are 1-2" calcium, I've sraped some off and dropped muriatic on it -- it fizzed up so confirmed on that. The plaster overall is also starting to feel rough/sandpaper like. So both nodules AND scale. It's a bummer.

I don't check hardness very often, and I was very surprised to see the 925 hardness number. My tap water is CH 240, my water softener has a CH of 0. I have not drained the pool since I bought the house 7 years ago. It's weird because I top off the pool with softened water starting a few years ago, but still have totally lost the CH battle.

THE PLAN???: I think I should drain the pool almost entirely, and refill with my tap water. I'm concerned that draining the pool will make the nodules worse because as plaster drys it can make micro cracks worse. I will try and scrape off and/or muriatic acid some of the bigger nodules as I'm draining the pool. I certainly can't just leave the pool at CH 925 right??

Does that sound about right? Anything else I should be doing here (besides testing my water more regularly)? I also don't brush my pool often enough. Probably only 3-4X per year. I guess I'm starting to pay the price for ignoring standard stuff.

Also, everybody else already knows this, but a reminder: test chemicals go bad. Part of my problem was using 5 year old testing chemicals and thinking that was "OK". In particular I think R-0011L went bad on me. I re-upped my chems from the TFP test kits store and numbers above should be accurate.

Thanks TFP peoples. This forum has been a lifesaver.
 
Last edited:

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,111
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
It is time to exchange the water to fresh.
Read the exchange section of Draining - Further Reading
With that level of CH and salt, it should be a pretty efficient exchange.

When you get the pool water exchanged, plan to maintain a CSI (get the number from Poolmath) of -0.6 to -0.3. See if that starts to resolve some of the scaling.

Using softened water for make up (not for the exchange) is good. Your CH was probably already very high when you started using the soft water. The big heat up times really drive your CSI high and that exacerbates the scaling.
 

wideload

Member
Apr 23, 2014
8
San Carlos, CA
Thank you both! Love the idea of the drain/replace at same time so I don't exacerbate my micro crack problems and keep my plaster wet. That sentence doesn't sound quite right lol.

Never heard of CSI before, I'll start to track this and keep the numbers in mind. Agreed, CH probably been way way too high for a while because i've been topping off with soft water for 3 years -- no wonder my pool feels like 120 grit sandpaper now. Thanks!
 

BenB

Gold Supporter
Jul 24, 2020
107
San Jose, CA
Hello fellow Bay Area person!

I just replaced the water in my pool for the same reason last month. 950-1000 CH! See my thread here on the subject.

A few thoughts based on what I learned going through it:

- Well timed, you can keep the time the pool is exposed to a minimum. Finding a cooler few days, watering the sides down regularly etc.

- Everything fizzes when you put acid on it. I'd read the same information you had, but was corrected. So you're no doubt correct that you have nodules and maybe some scaling, but the acid test itself isn't that helpful

- I tried to mini acid wash a few nodules. As careful as I was, it created a dark patch around where I had scrubbed. I was later advised that wet/dry sandpaper is also effective at smoothing out noodles. In retrospect I should have done that as I think the look would come out better.

- If you are 100% sure that you have widespread scale as well as the nodules, then the 'no drain acid wasn't or 'zero TA' method would be better than washing while empty. However, this will damage your plaster at the same time and you will need to time it very very carefully.

Definitely get PoolMath and use it to track your chemistry going forward. It calculates CSI for you. Over a long period of time with fresh water and negative CSI you might just remove some of the wrist of it.

Good luck!
 

wideload

Member
Apr 23, 2014
8
San Carlos, CA
Thank you BenB and others.

I'm gonna start this "no drain water exchange" project soon (Draining - Further Reading). My pool temp has finally dropped to 79. My muni water is 72.

Pool math says to go from 925CH to 350CH, with municipal water at 240CH, I need to replace 84% of my water, which would be 11,000 gallons. The pool math app says **replace** 11,000 gallons. Obviously I'm not replacing when it's the "no drain" method. So the wiki article above says to do 5-10% more. So we'll call that 7.5%, so now I've got to drain/replace almost 12,000 gallons. Should take about 24 hours.

I have not measured how many gallons my 1/3HP sump pump moves but I will soon. The wiki link says expect 7.5gpm. I've got sump pump in the deep end and my muni water hose in my skimmer (not sure of the logic of that beyond trying to put water in the pool "gracefully" to not intermix water)??

Will turn pool pump off obviously.

Anything else I'm missing? Wiki says to do it all at once so I guess I'll take that advice. I've got my chlorine high right now (10) because I'm worried that with no pump/circulation, it's gonna drop a lot during this process (I've fought algae probs and I do NOT want to go down that road). I've got CYA on order and gonna get some more chlorine/muriatic tomorrow.

Ugh, feel like Patton getting ready for war. Anything I'm missing here and/or numbers I munged? You guys/gals are the best. I felt like I really knew "most" of pool management but here I am, tackling yet another first. Thanks!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,111
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
(not sure of the logic of that beyond trying to put water in the pool "gracefully" to not intermix water)??
Exactly.
I've got sump pump in the deep end and my muni water hose in my skimmer
Pool water is warmer than the fill water. But high CH. Your system is nearly balanced so you may have some mixing.
 

wideload

Member
Apr 23, 2014
8
San Carlos, CA
Very cool to see this working. I've been running for about 7 hours now. Center pool sample is now CH 600 (down from the CH 925). Took sample of the sump pump water: CH 837. So obviously, there's some mixing going on but ya, it's working!!!

Pool level has hardly moved at all. Had to run two hoses IN to match the sump pump OUT. But all good!! Thanks all :)
 
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wideload

Member
Apr 23, 2014
8
San Carlos, CA
All done! Re-balancing water now. Middle depth of pool was CH 325. Sump pump out was CH 375 at the bitter end. Pool pump is back on I'm sure I'll wind up w/ something in the middle, which is almost perfect I think.

Already got the FC up (was at zero, should've added some earlier). Hopefully that won't lead to a problem, I've already got it 6. Adding CYA, salt ..... whehew. Lots of work thanks again for this amazing community!
w
 
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BenB

Gold Supporter
Jul 24, 2020
107
San Jose, CA
Good job! It's a real whirlwind throwing everything in there to start mixing up isn't it? I felt like I was on a mission against time to get the chlorine up, pump running etc when the refill was done :)

Expect to have some cloudiness for a couple of days while the new water settles down (might not be an issue since you used a gentler refill method with fewer bubbles etc). Also give it a couple days with the SWG off while the salt fully disperses.

You'll be swimming in no time!
 

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