Mustard SLAM not working

[Jdlsc]

Hello! I bought a house last August and had to do a 5 day long slam to rid the pool of the previous owner's algae. Once the SLAM was done, all I had to do was bump up the TA some and all has been well since. The CYA was at 50 initially and I let that slowly drop through the back washing and draining due to heavy rains since then. It's finally settled down to somewhere between 30 and 40. I've been treating it as 40 and targeting 8 daily with my Walmart bleach additions.

I didn't close the pool over the winter so getting it ready for this swimming season has simply been a wait for the temperature to rise. We've been swimming for 5-6 weeks now.

I've noticed a yellowish ring forming along the perimeter of the pool and thought I had mustard algae. The vitamin C trick had no effect so I don't believe it's metal stains.

I'm 18 hours into my Mustard SLAM (brushing and checking then adjusting up FC every 2 hours except after the sun went down). After waking up this morning I was disappointed to see that the process so far has had no effect on the stains. Brushing seems to do nothing. Prior to the SLAM I've tried brushing these stains vigorously with no effect.

Could these be metal stains? I've only used the TFP method since I've owned the house so I know I haven't added any metals. Who knows what the previous owner put in the pool. He left a myriad of dusty old chemical bottles that all went in the trash, except for the Muriatic Acid.

Here are my test results from just prior to the Mustard SLAM.

PH 7.7 (lowered to 7.2-7.3ish immediately before SLAM)
FC 4
CC 0
TA 110 (seems high but my PH rarely requires any adjustment up or down. It's rock solid)
CH 75
CYA 40

Any advice? Could these stains be metal stains and not mustard algae? If metal, is it typical for stains to develop after 4-5 months of no staining and no metals being added? I first noticed the stains slowly forming over the winter when the water was cold. I continued to maintain chemistry over the winter although chlorine additions were only required every 10-21 days.

Finally, I don't have any numbers, but I'm fairly certain my city water is mostly metal free. We're fortunate to have a good supplier.

Attempting to add photos...

 

[Jdlsc]

Now that the photos have uploaded, the stains are difficult to see. They're barely visible along the perimeter. The stain is approx 3" wide around the perimeter.

 

[zea3]

Mustard algae grows in shady areas of the pool, it is unlikely a stain would distribute even around the bottom. Did you have any leaves accumulate in the pool over the winter?

 

[Jdlsc]

The newness of maintaining the pool is still strong. I wouldn't say there was any excess accumulation over the winter; I'm anal about keeping it clean still.

I didn't know about the shade preference of mustard algae.

Since it's looking certain this isn't mustard algae, what's the best way to get stains off of vinyl?

I have mostly oaks and large river birches near the pool. During the oak pollinating I had a lot of the fuzzy/stringy oak pollen things for a couple weeks. About 2 weeks after that ended, the river birches started shedding their little oatmeal looking seeds. That **** lasted about a week. Maybe this caused the staining?

 

[AimeeH]

Hi there

If you suspect metal stains try holding a vitamin C tablet on it to see if that lifts the stain. If it's metal that may lift it and to prevent it you'd need to do an ac orbit acid treatment and use a sequestrant.

 

[Jdlsc]

Hi there

If you suspect metal stains try holding a vitamin C tablet on it to see if that lifts the stain. If it's metal that may lift it and to prevent it you'd need to do an ac orbit acid treatment and use a sequestrant.

I tried the Vitamin C tablet and it had no effect on the stains. I'm now thinking these are stains from the leaves that fell during the cold months. I was pretty good about getting them raked up and skimmed out, but I guess not good enough.

 

[zea3]

It could be tanins from leaves and pollen. It will fade over time at normal chlorine levels.