Calcium deposits?

[jesper]

I’m having issues with what I think is calcium deposits, they are found on the bottom of the pool below the returns and on one of the steps. See photo



After running the dolphin robot it’s filter was full of what I think is calcium deposits



The pool is a 2 month old beadcrete in-ground pool where the steps and bench are genuine marble.

I use a SWG for chlorination and an automatic acid feeder to keep pH balanced, the pH feeder is controlled by a pH probe in the pipe after the filter. The installer provided the initial liquid acid, 40% sulfuric acid, notice not muriatic acid, is that an issue?

Measurement data from today:

FC 9.5 target 7
CC 0.5
pH 7.4
TA 110
CH 400-425
CYA 90
SALT 4000
TEMP 32 Celsius / 89 Fahrenheit

PoolMath app reports CSI -0.11 with the above, so if anything I should have issues with dissolving calcium from the beadcrete plaster and marble steps.

In addition to the calcium deposits I also noticed that pH is drifting upwards. The automatic acid dosage system have added 1.5-2 litres of 40% sulfuric acid the past 12 days.

If I lower TA to 80 as recommended PoolMath says my CSI becomes -0.30, if I also raise pH to 7.6 it becomes -0.12

What do you recommend, lower TA to 80 by aeration and then raise pH to 7.6 ? Any other ideas?

 

[JoyfulNoise]

You absolutely should not use sulfuric acid in a plaster pool with an SWG. What you’re seeing is calcium sulfate scale. Sulfates are bad for plaster and SWGs.

 

[jesper]

Thanks a lot! I’m not surprised this pool installer messed up in yet another way ... have had a series of issues with them.
I’ll go looking for some muriatic acid to use instead.

How about the TA value and the impact on CSI? Is it a good idea to lower TA and raise pH keeping CSI slightly negative?

 

[jesper]

It will be a couple of days before I can get some muriatic acid, do you think I’m better off turning off the automatic acid dispenser and let the pH value creep up?

Maybe set the target at 7.8 instead of 7.3 so it will not dispense any acid unless the pH goes up a lot?

 

[ajw22]

How about the TA value and the impact on CSI? Is it a good idea to lower TA and raise pH keeping CSI slightly negative?

Yes. See Recommended Levels - Trouble Free Pool for plaster pool with SWG. Low TA and higher pH works best. SWG pools can be happy at pH around 7.8

 

[ajw22]

It will be a couple of days before I can get some muriatic acid, do you think I’m better off turning off the automatic acid dispenser and let the pH value creep up?

Maybe set the target at 7.8 instead of 7.3 so it will not dispense any acid unless the pH goes up a lot?

Even letting your pH drift up above 8 will be fine for a week or two. No damage will happen with a high pH for a short time. I would rather do that then dump more sulfuric acid into the water.

 

[jesper]

Even letting your pH drift up above 8 will be fine for a week or two. No damage will happen with a high pH for a short time. I would rather do that then dump more sulfuric acid into the water.

Thanks I’ll change the pH target to 7.8 until I can get some other acid

 

[jesper]

You absolutely should not use sulfuric acid in a plaster pool with an SWG. What you’re seeing is calcium sulfate scale. Sulfates are bad for plaster and SWGs.

I'm having issues finding hydrochloric acid in a suitable low concentration, I can get it in 32% concentration that likely will be too strong for my peristaltic pump.

The pool companies I've checked here, all use liquid sulfuric acid or dry sodium bisulfate, that essentially is sulfuric acid as well. Before the pH control with the peristaltic pump was installed, I used dry sodium bisulfate, which explains why I've been having the issue with the scale deposits from the beginning.

I'm somewhat worried about diluting the 32% hydrochloric acid myself, it is very strong stuff that is potentially dangerous.

 

[JoyfulNoise]

Sulfuric acid is far more dangerous than muriatic acid. While the fumes from muriatic acid are a bit harsh on the nose, they are in no way dangerous (your nose has a low odor threshold for HCl). Sulfuric acid can cause rapidly forming burns on the skin with severe and deep tissue damage while HCl can be splashed on the skin and take several minutes before anything is felt. One should always use splash proof eye protection when handling acids of any kind.

 

[jesper]

So you would not be worried about having to dilute a 32% HCI to 10-15% assuming proper protection is used ?

 

[ajw22]

So you would not be worried about having to dilute a 32% HCI to 10-15% assuming proper protection is used ?

Always pour the MA *into* the water, not the water into the MA.

@Dirk dilutes his MA used in his Intelliph setup. He has posted on how he does it.

 

[jesper]

Always pour the MA *into* the water, not the water into the MA.

@Dirk dilutes his MA used in his Intelliph setup. He has posted on how he does it.

Thanks, yes I did know that must always add the chemical to water, not the other way around.

I'm still a bit nervous about diluting it myself, looking at a safety data sheet it looks kind of scary. Amongst other things, it says only use in well ventilated areas. My pool equipment is located in an underground concrete "basement" next to the pool, the only ventilation it has is two 100mm (4 inch) vent pipes where one of them has a humidity controlled fan. I could run the fan continuously, but not sure it would count as well ventilated. Access to this "basement" is via a hatch in the deck surrounding the pool, the hatch is normally closed.

Obviously I would do the mixing outside in free air, not in the equipment "basement", once mixed would there be any significant difference between the vapour release danger of 10-15% hydrochloric acid vs. the 40% sulfuric acid I have today ?

The sulfuric acid comes in a 25 litre tank, where I just need to unscrew the cap and screw in the special cap with a hose to the peristaltic pump. The chance of spilling or getting into contact with the acid is significantly less than mixing concentrated hydrochloric acid through a funnel into a tank partially filled with water.

Regarding protective gear, would wellington boots, long rubber gloves, rubber apron and full coverage face shield be considered sufficient ?

 

[jesper]

I’ve been thinking how to contain acid vapours, what if I use two containers like



Where the acid vapours are trapped in the cavity above the liquid acid in one container and water mixed with a base in the other. I don’t have issues with vacuum when acid is removed by the acid pump as it can draw air through the vent pipe.
Only issues with acid fumes is when refilling, I could do that through a hose from above ground if I have a valve on the fill pipe. Though in this case we might push some water/base mixture out through the vent pipe, maybe it is better to just fill in the equipment pit/basement and make sure I ventilate very well. I could dilute the acid outside and fill with already diluted acid.

What do you think?

 

[Dirk]

I'm actually still experimenting with the best way to mix my water and acid. I've poured both into my tank, then, worrying about how well they actually mixed, I run a wire affixed to my drill into the tank to give it a good stir. This works well. Once, I mixed them together in a bucket first, then poured the bucket into the tank. I ended up spilling some on my concrete and foot. It fizzled the concrete, and while I felt it on my foot, I didn't get burned. But that ended the bucket experiment.

Some here will call me over cautious, but I wear chemical gloves, a chemical mask and eye protection. I believe muriatic acid is not horrible on skin, but I also believe that it can cause serious damage to soft tissue (especially eyes, but I think lungs, too). Because I don't have to handle it all that often, I feel good about it to be on the safe side. It's relatively easy to protect eyes and lungs, why not do so? Murphy's law dictates that that one errant drop from a splash will target your eyeball!!

For what it's worth, I get my new hearing aids tomorrow... I damaged them over the years to the extend that this is now my fate. I never had any one dramatic event, just years of small amounts of abuse. I now regret not being more careful with my ears, I won't make the same mistake with my eyes and lungs, regardless of how unlikely permanent damage might be...

 

[Dirk]

Oh, I only use muriatic 31% and dilute that 1:1 with water. That's my pump manufacturer's recommendation. Alternately, I could just buy the 14% acid and just pour that into my tank as is, but I think I'm saving some money by mixing. At some point I'll probably cave and just use the 14% and eliminate having to mix at all...

 

[jesper]

I got long chemical gloves, protective glasses and a face mask as well. I too prefer to error on the side of caution

 

[Dirk]

Personally, I don't trust any sort of pH-reading equipment. I passed on IntelliChem for that reason. Even with that kind of automation, you still have to test your water, to make sure it's working correctly, so for my use-case, it made no sense. Why complicate things, why add even more electronics that can fail? I set up the chlorine and acid gizmos to get me close to perfectly balanced water, most of the time, and test once a week to make sure they're working. If I have to, I either tweak their settings a bit (as weather and pool use demand), or just add small amounts of chemicals manually to fine tune. It's relatively foolproof, and I know it's working because I test the water with a good kit to confirm it. There's no such thing as a maintenance-free pool. But I think with my MO I've got mine as close as is possible.

 

[jesper]

Personally, I don't trust any sort of pH-reading equipment. I passed on IntelliChem for that reason. Even with that kind of automation, you still have to test your water, to make sure it's working correctly, so for my use-case, it made no sense. Why complicate things, why add even more electronics that can fail? I set up the chlorine and acid gizmos to get me close to perfectly balanced water, most of the time, and test once a week to make sure they're working. If I have to, I either tweak their settings a bit (as weather and pool use demand), or just add small amounts of chemicals manually to fine tune. It's relatively foolproof, and I know it's working because I test the water with a good kit to confirm it. There's no such thing as a maintenance-free pool. But I think with my MO I've got mine as close as is possible.

I got it as part of a kit, and in this particular application there is no way to say "run acid dose at X percent, or for N minutes a day". But yes, I agree that you still have to test the water and make any corrections. So far the pH probe has been reliable, my Taylors K2006 testkit consistently reports 0.5 to 1 higher than what the pH probe says, so I just set a target slightly lower than the actual pH I want, and it works. Of course, I've only had this a couple of months now, so I cannot speak for the long term reliability of the probe. The installer said as long as it doesn't dry out (which it will not in my install, as it is below the water line), it should last a minimum of 3-5 years.

 

[Teald024]

Have you checked the chemical resistance charts to see if you need to dilute the acid? What model peristaltic pump do you have? What materials are used in the hose from the tank to the pump and then pump to the plumbing? What tube material is in the peristaltic pump? If the tube & hose material can handle the HCL 20 Baume/31% acid, then I don't see the point in trying to dilute the acid. Post the materials and we can check for you.

 

[jesper]

Have you checked the chemical resistance charts to see if you need to dilute the acid? What model peristaltic pump do you have? What materials are used in the hose from the tank to the pump and then pump to the plumbing? What tube material is in the peristaltic pump? If the tube & hose material can handle the HCL 20 Baume/31% acid, then I don't see the point in trying to dilute the acid. Post the materials and we can check for you.

Thanks for the interest, the manual for the Etatron B3-V peristaltic pump says (direct link, with the english manual starting at page 9)

2.3 Materials in contact with the additive

Hose:
Norprene
Nipples:
Polypropylene
Filter:
Polypropylene
Suction tube:
PVC
Discharge tube:
Polyethylene

The Norprene tube in the pump itself doesn't appear to be rated for concentrated hydrochloric acid a per this link, that says
Hydrochloric acid (dil) A
Hydrochloric acid (med) B
Hydrochloric acid (conc) —

For the 1st column that is PN = PharMed® BPT, High-Pressure PharMed® BPT, PharmaPure®, Norprene®, Norprene Food

Ratings
A: No effect; little noticeable change
B: Minor effect; slight corrosion or discoloration
C: Moderate effect; not recommended for continuous use; softening, loss of strength, swelling and/or shrinkage
D: Severe effect; not recommended for use; severe softening, swelling and/or shrinkage
—: No data available

And this is data for 21 degrees C or 70 degrees F, my machine room is ~35 degrees C

Based on this, I think I better dilute it to ~10%