Baking Soda Stains on Plaster

[Mbb04]

Just to give you a bit of backstory I've had my pool up and running for about 3 months now and the whole time I have been battling PH rising above 8 in short periods of time(checking every 2-3 days). All other test results were in a good range(TA: 80-90, Chlorine: 3-5, Calcium Hardness: 360) except for the CYA which had been really low(sub 20) I finally added stabilizer a few weeks ago and ran my pump overnight per the instructions on Pool School. It helped get my CYA up to 45, which i need to do again to get it over 60, but in the process my TA dropped to 30. I added baking soda 2 weeks ago and got it to 50. When i added it some settled on the bottom and i just brushed it off a few minutes later without any issues. I added more baking soda last week and immediately scrubbed the bottom. I got in the pool the next day and there were two white stains on the bottom where the baking soda settled. Has anyone ever seen this happen before? Any suggestions to clean it? I saw using an acid mixture could work but will spraying underwater even be an option. I haven't dove in and tried to scrub with a brush, which is going to be my first attempt but wanted to see if anyone on the board had experience with this problem before.

My readings seem to be in good order, minus raising the CYA a bit:

Chlorine: 7
PH: 7.6
TA: 80
Calcium: 360
Salt: 3600

 

[ajw22]

@mknauss any thoughts on the baking soda stains?

 

[Mbb04]

@mknauss any thoughts on the baking soda stains?

I tried scrubbing it today and tried squirting some acid/water mixture with no success. Looks like two pebbles covered in calcium or some type of build up. Will try to get some better pics tomorrow morning when the wind isn’t blowing.

 

[JoyfulNoise]

Baking soda in excess like that will create an area of high pH and high bicarbonate concentration. It will lead to scaling. Your CSI right around the baking soda pile was probably off the charts positive. Give it time with negative CSI water and it will slowly dissolve away. You could try acid scrubbing it but that's likely to cause more damage than it's worth ...

 

[Mbb04]

Baking soda in excess like that will create an area of high pH and high bicarbonate concentration. It will lead to scaling. Your CSI right around the baking soda pile was probably off the charts positive. Give it time with negative CSI water and it will slowly dissolve away. You could try acid scrubbing it but that's likely to cause more damage than it's worth ...

Appreciate the info. I guess i live and learn, didn’t even realize that could happen. I have a little scaling I’m dealing with on my waterline tile at my spa spillover so I am trying to keep my CSI under 0

 

[JoyfulNoise]

Appreciate the info. I guess i live and learn, didn’t even realize that could happen. I have a little scaling I’m dealing with on my waterline tile at my spa spillover so I am trying to keep my CSI under 0

You can go below -0.3 for a time if it helps to speed up the process.

 

[Mbb04]

You can go below -0.3 for a time if it helps to speed up the process.

Whats crazy is it was running at -1 for a day or so before I bumped up the TA the first time. My TA plummeted from 80 to 20 after I ran my pump over night getting my Cya up. I got my TA up to 50 and tried raising it to 80, which was probably not necessary, when those stains happened.