discolored spot in pool

[StYang]

This is a 15 years old pool, I have owned it since last year. I use the method I learned from this website to maintain my pool.
The most recent test data is like this
- Location:Texas
-Chlorine : 10 (only add liquid chlorine from local Pinch A Penny store, twice a week and about 0.8-1 gal each time recently)
-PH:7.6 (need constantly add acid to lower PH value)
- Stabilizer: 60
- TA: 100
- Calcium:220 (this is slight low and i didn't do anything about it

Everything is fine, no algae, nothing I noticed abnormal until recently I notice some discolored spot in the pool bottom, only a small area as shown in picture. it feels like some kind of corrosion, the surface is not as smooth as other area
The reason I think maybe
- the discolored place is mostly located at where I usually pour liquid chlorine, sometime I poured liquid chlorine in early morning before the pump starting time therefore that area may have high chlorine for a while sometime.
- Is it because the calcium is low in my pool? The calcium is a little low and I didn't do anything about it

Any suggestion? Can I do anything or replaster is the only solution?

 

[YippeeSkippy]

Hi there....welcome to TFP posting.

Have you ever poured Muriatic Acid in that spot? It can lay heavy on the bottom if water from a return isn't carrying it away and diluting it. And I personally always brush when using that.

I'm not sure if liquid chlorine would cause that but powdered can.

Have you added any of those things?

Maddie

 

[StYang]

Thanks for your reply.

I never directly pour muriatic acid to pool, always dilute it in a big bucket of water first
I only directly pour liquid chlorine to pool

 

[Mike1162]

Why aren't you running the filter while adding chlorine & why are you only adding twice a week? Most of us add daily.

 

[StYang]

i need go to work in the early morning when the pump is not on....I can correct that by changing the pump timer.

 

[mknauss]

always dilute it in a big bucket of water first

It is not necessary and added risk to dilute muriatic acid in a bucket.
Simply pour it slowly at the return jet with the pump running. If you like, brush the area to disperse.

 

[StYang]

instruction label of the muriatic acid says to dilute it in a big bucket of water.....I will double check. Thanks for your reply

 

[mickey4paws]

i need go to work in the early morning when the pump is not on....I can correct that by changing the pump timer.

Good idea, you should definitely have your pump running first and then add your chemicals.