Dark spots reappearing on pebble tec

[blantonpool]

Hi, I completed a SLAM about 2 weeks ago which I started because the walls of my pool were getting dark and I was getting dark areas on the pool floor. After lots of steel brushing during the SLAM, things were looking good and I met all 3 criteria for ending the SLAM. However, dark areas keep reappearing. The spots go away if I put some cal hypo on them so I know they are organic. What could these spots be that don’t seem to go away?

Tests using Taylor K-2006C:
FC 8.8
PH 7.3
TA 110
CYA 71
CH 350

 

[Texas Splash]

Welcome to TFP! As you noted, they seem to be organic since they react well to the cal-hypo. Now it would appear something is falling onto the water and sinking to cause stains. I can't really see the stains well in the pic. Do you have lots of trees nearby maybe? Were the stains the only reason you did the SLAM, or were you seeing algae and/or losing FC rapidly as well?

 

[blantonpool]

I do have some pines and palms nearby but I run my robot in the pool every day so things don’t sit on the bottom for long. The SLAM started because of these spots on the floor and also because the walls were getting very dark on about 1/2 of the pool. So I steel brushed the walls and floor every day during the SLAM and it got significantly better. The odd thing with the spots is they tend to come back in a similar spot. The pictures attached are from before/during the SLAM to show you what it looked like at its worst. I also realized right before the SLAM that my CYA was really high (about 100) and my FC level was not adequate which is likely what caused this whole thing. Thought maybe it was black algae.

 

[Texas Splash]

Organic seems to still be one predominant, and perhaps the only, real factor. But just out of curiosity, are you on well water? Have you tried rubbing a Vitamin C tablet on any stained area as a comparison?

 

[blantonpool]

Yes I tried that to make sure it wasn’t metal staining and it didn’t make a difference. My copper levels are there but low: .2ppm

 

[Texas Splash]

Are you using the PoolMath APP? If so, it's not linked here to TFP so we can't se your water testing history. That might help to see the history.

Also, perhaps post a couple pics of your equipment pad since your signature is blank.

Last, how old is your pool/pebble?

 

[blantonpool]

Yes, I am using pool math now but that only started about a month ago when I discovered TFP: PoolMath Logs

The pebble is 14 years old

Pics of my equipment attached

 

[Texas Splash]

Do you have a heater installed? If so, what make/model?

Create Your Signature - Further Reading

www.troublefreepool.com

 

[blantonpool]

Yes, I do - it's a Aquacal SQ120 heat pump. Just updated my signature, thanks for sending that link

 

[Texas Splash]

Yes, I do - it's a Aquacal SQ120 heat pump.

So even though everything thus far tends to point towards organic, there's a part of me concerned about potential copper leaching - if your heater has a copper element. I am going to invite @JamesW for another set of eyes just because it seems odd you've had such extensive staining (with a decent FC level) and at some given points the pH appears to have dipped a bit low, so I'm worried about any potential corrosion impact to the heater. Let's see what James has to say.

 

[blantonpool]

I thought the same - 2 months ago I took a sample to Leslie’s and copper was .6ppm, iron 0 ppm. I drained about half the pool and refilled and put a culator in and it’s down to .2ppm as of a few weeks ago. The old heater that died was a gas heater with a copper exchanger - which is where the copper came from. My current one has a titanium heat exchanger. Since the vitamin c didn’t do anything and cal hypo does work, I ruled out metal staining