Do I Have an Algae Bloom

[Junta]

Hi Everyone! I am trying to determine if I have an algae bloom. My water is crystal clear. It looks good. My biggest issue has been that I can’t seem to get the pH lower (it’s on the verge of high) and the TA higher (it’s on the verge of low). No sign of algae on the steps. about three or four days after vacuuming, I see this fine, black sediment on the bottom. My pool is located on the edge of the woods and I always assumed this was just stuff from the trees. Years ago when I first started with my pool, I had algae blooms but it was obvious and green. I shocked my pool yesterday earound 4:30 and at 11:00, I measured the chlorine and it was 18 ppm. This morning I checked it and it was 16.5 ppm. The difference is greater than the 1.0 difference when looking to complete a successful SLAM process. Am
I catching this in the early stage of an algae bloom? Or am I just being paranoid about one? Thoughts? Thanks for the help!

My latest test results from this morning:
pH: 7.8
FC: 16.5
CC: 0.0
TA: 85
CYA: 50

 

[HermanTX]

You do not indicate how you chlorinate your pool. Is it with use of liquid chlorine?
When did you test your FC 18ppm - was that after 11pm and after the “shock” had mixed for at least 30 minutes?
Did you do the morning test prior to sunrise or before your pool was hit by direct sun?

Assuming that it was a proper Overnight Chlorine Loss Test then you could have start of algae even though your CC is zero.
For CYA of 50ppm your SLAM level is 20ppm FC.
Not sure how you got TA of 85 as the TF-100 kit uses 25ml sample and multiple # of drops by 10 - so most likely a TA of 90
MA should reduce both pH and TA - you just have to continue to work the process to lower both, let pH rise and then lower both again until you get to TA that you want or the TA that the pool is happy.

If you have any doubts, I would go to SLAM level (maintain throughout the day) and continue to do Overnight Chlorine Loss Test. Also, bring your pH to 7.2 or so before SLAM starts.

Also, for general maintenance (after SLAM) it is best to maintain your FC at a consistent level through the day - this is range of 6-8ppm for CYA of 50.

 

[Homebrewale]

At your FC level, the pH test would be inaccurate.

 

[Junta]

I use liquid chlorine.

I shocked around 6:00 PM and wasn't able to test until 11:00 so the overnight test result is probably inaccurate. And my test this morning was around 6:00 AM well before the sun hits the pool.

I am going to go ahead and SLAM. Seems like the best course. I was hoping to avoid it but not that big a deal.

I appreciate the help.