Calcium Spots or Black Alage

Bridgetalford

Member
Mar 12, 2016
11
Ponce de Leon, Fl
I have been dealing with these hard white/grayish spots on the bottom and walls of my concrete pool. I am in the middle of a SLAM/MUSTARD algae shock as we speak. The reason for this is that I did also have some issues with algae. I recently connected new Intellichlor salt water system and assumed it was not working as I could not keep any FC when running at 100%. Based on my CYA of 70 (this test is so hard to determine if truly accurate), I began slamming the pool at 28. I ran this for approximately 48 hours. Then switched to the higher levels of 40. It has been running now for about 36 hours at mustard algae level. The algae does appear to be gone, but the hard deposits remain. Last night I was at 40 on chlorine and this morning when I tested I was at 30. I added more chlorine this morning to bring it back up to 40 and when testing just now, I have already fallen again to 31ppm in a matter of 3 hours. Is it normal to have a such a large drop in chlorine in such a short amount of time?

Last year when I dealt with these hard deposits, I tried using a pumice stone to scrap them down with very little improvement. I also used a hose and poured some muratic acid on them, which did appear to help more, but I would not say it totally eliminated them, as I didn't want to leave it over the spot for too long for fear of damaging the plaster. Can someone confirm exactly WHAT you think these spots are? Is it simply Calcium deposits, or is it black algae? Should I continue at mustard algae levels until the chlorine does not drop more than 1ppm overnight?

My CURRENT numbers are posted below, but keep in mind, they could be off as I have read that when Slamming the pool your PH and alkalinty for instance isn't accurate. This seems to be accurate as shown by the readings I just got.

FC - 31
CC - 0
PH - 7.0 (could be lower as that is as low as color goes) off due to shock
ALK - 40 (only changed from green to blue - did not get pink color - due to shock?
CYA - 60 (when I began SLAM is was at 70) **This test is very subjective in terms of seeing little dot
CH - 290

When I had my water tested at the pool store they said my calcium was at 225. Gave me calcium to add. I did add several pounds and got it up to where it is now. I thought high calcium caused the scaling, not low calcium.101170
 

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onBalance

TFP Expert
LifeTime Supporter
Jul 25, 2011
931
Utah
I would like to see more photos of the spots, but they do appear to be very small calcium nodules (as Richard pointed out). That means that the delamination issue is minor and small. And yes, it can take many years for that to happen. Try sanding the nodules with 100 grit wet and dry sandpaper, and plug the small hole with epoxy cement. Nodules will form regardless of what the water chemistry is.
 

Bridgetalford

Member
Mar 12, 2016
11
Ponce de Leon, Fl
I would like to see more photos of the spots, but they do appear to be very small calcium nodules (as Richard pointed out). That means that the delamination issue is minor and small. And yes, it can take many years for that to happen. Try sanding the nodules with 100 grit wet and dry sandpaper, and plug the small hole with epoxy cement. Nodules will form regardless of what the water chemistry is.
Here are a few more photos. Why the dark area around the white nodule?14967421-8833-4907-80AB-BB18E17BB5C9.jpegF057D701-4080-4B55-99B5-E4B395CAF847.jpegF2562EC4-A676-4221-9D79-8B61503658BE.jpeg
 

onBalance

TFP Expert
LifeTime Supporter
Jul 25, 2011
931
Utah
Nodules are very porous and rough which helps dirt and metals to become easily attached to the forming nodules.
 

Bridgetalford

Member
Mar 12, 2016
11
Ponce de Leon, Fl
What would you recommend I use to remove? Should I do muratic acid over each spot using a pole and hose? I saw some thread on lowering the TA to 0 and that might help to remove them.