WHOA! Can a shock for algae only lose 1 ppm overnite? Was it algae?

[Lynnster52]

Here's an odd one.
After maintaining clear, sparkling pool since opened in April (new to TFP this year) this happened:

Yesterday afternoon, after a sunless day, I noticed what looked like algae (on slant wall to deep end, on bottom here & there, & also on shaded slants of deep end walls).
MUST BE ALGAE...better shock!

5:30 pm:
FC 3 (30 hrs earlier, FC was 4)
CC 0
PH 7.8
TA 80
CYA 40 (just in the past week, we finally got a reading above the 30, with dot disappearing after using just 2 tri-clor pucks in a floater for a month. They were removed once we got this reading)
temp 77º (had been 85º prior but got cooler/sunless days recently)

Worried about algae, I immediately added 1 gal of 8.2%, knowing I needed more to shock, but paused to brush like mad & saw clouds of yellow or greenish/yellow pale brown something (hubby & I disagree on the color). Pool is next to dirt ballfield & it's been dry/breezy, & we also have large shade trees near pool dropping stuff, so not certain)

Before I could say "wait I need to finish shocking", hubby turned off pump & cleaned filter, so pump was off for 30-40 mins. When back on, I retested to get math to finish shock:
6:30 PM:
FC 8 (looking back, no way did the gal of bleach completely circulate & FC had to still be rising due to pump being off most of that hour)
CC 0
PH 7.8
So, not thinking about lack of circulation time, I calculated PoolMath as FC at 8 ppm with shock goal of 16 ppm. And added recommended 340 oz of 8.2%.

8:30 PM (2 hrs later)
FC 21.5 ppm
CC 0
PH 7.8

TODAY (next day) 8 AM:
FC 20.5
CC 0
PH 7.7

Question: If we had algae, wouldn't the FC have gone down more than 1 ppm overnight?

The pool is sparkling in the sun today & nothing has settled back down on the walls/floor/slant....yet.
I don't think pool needs a SLAM (water is crystal clear, no CC and no visible algae)

12:30 PM:
FC: 17 (It's hot & sunny today. Can FC drop 3.5 ppm in 3 1/2 hrs in hot sun, or is this a delayed gobbling of algae?
CC 0

3 PM TODAY:
FC 14 (another drop)
CC 0
PH 7.8

To be truthful, we hadn't vacuumed or brushed in a month. The occasional tree stuff gets scooped with net.
What am I missing besides the stupidity of shutting down pump yesterday amid shocking & taking next reading too soon? Why no big ppm drop overnite & then finally dropping quickly during day today? The sun just left and it's now pouring out.
I also realize that now that we are getting a CYA reading, I need to maintain a higher FC reading than I was and perhaps this is why we got a bloom, if that's what it was?

Tks for your thoughts!

 

[Divin Dave]

As new pool owners, we all worry ourselves to death. Especially when we see pics of swamps by others on the forum.
So, first thing to do is relax and try not to be so anxious.

So, one thing you didnt mention, is how have you been maintaining FC up until the point where you decided you had algae?
This is more important in my mind, than what happened afterwards.

If you maintain your FC/CYA of between 7.5 and 11.5%, then you won't get any algae.

From all indications, and your test results, you're good on the mini SLAM you did.

 

[Lynnster52]

Tks Divin Dave. Not a new pool owner (pool is 30 yrs old) but new to TFP this year!

I've been maintaining FC by testing daily & using PoolMath. Water was not allowed to go under minimum FC, which was 3 until CYA finally went to 40 the other day. But lately I've been trying to keep pool around 5-6, not 7.5 as suggested so maybe that's where I went wrong?
Pump runs 24/7.

It's 11 pm (8 hrs since last test) & FC is 7.5 & CC 0.
No sign of algae or whatever it was.
I probably should be adding bleach before going to bed, but I'm tired & brain dead so doing nothing until am for fear of screwing up again. Hope it doesn't drop too much by am!

 

[Lynnster52]

FC held at 7.5 overnite so I'm thrilled!

On a side note, since opening 6 wks ago, CYA was always under 30, but rose (very slowly) via 2 tri-chor pucks in floater, replaced as needed.

CYA hit 40 last week & pucks were removed.

To me, 40 allowed option of using pucks in auto-feeder when we go away for a couple of days.

Today, a week after removing the pucks, the CYA is 50, so still rose without pucks!

Is this rise in CYA expected due to to the slow process of using a couple of pucks as I was? If yes, how long should I expect CYA to continue to develop?

How often should I test CYA with such a rise in one week like this? I know I seem obsessive but new to TFP this year & don't want to screw it up.

P.S. I've added nothing else to the pool except daily 8.2% bleach as per PoolMath, keeping FC in target & never below min FC. As of this new 50 CYA reading, I will try to keep FC around 8 (have grandson with sensitive skin (& he takes daily chemo for leukemia) so for me it's extra scary wrapping brain around this new process of high FC/CYA after 30 years of OTO & keeping FC at 2 ppm!)

TODAY:
FC 7.5 (about to add 8.2% for new 50 mark CYA reading today)
CC 0
PH 7.7
TA 80
CYA 50

Tks!