Possible black algae

Trevor916

Member
Sep 15, 2020
12
Roseville, CA
Have had the pool a ~5 months. After reading the forums things were smooth sailing and water has been clear - Up until I got a little lax over the past month and didn't do my routine brushing maintenance . It had been maybe ~2-3 weeks since last brushing (shame on me), although I've been keeping my water chemistry in check thinking that was enough and water has been clear. This past weekend I went outside to do some yard maintenance and saw the pool, which seemed to have some darkish black stains I've never seen before on the bottom. (2 separate spots, both about 5 feet by 7 feet each, spotty in nature). Didn't get a chance to take pics unfortunately, but immediately tested the water and came up with the following;

FC: 10.5
CC: 0
pH: 7.5
CYA: 100
TA: 100
CH: 500

Did some research here and confirmed what i was hoping to avoid, even with good water chemistry you can still develop algae without proper brushing maintenance. Did a small step up in chlorine addition as well as a thorough brushing (nylon) which brought up some expected small clouds, although mostly grayish in color. Seemed to be more sediment/dust than anything else. The following day I purchased a hybrid nylon/SS brush to go at it again hoping to break up anything that might be there, thinking if it was algae I would see my CC results rise.

I've been brushing daily, stain seems to be slowing dissipating, but my water results still have me a bit puzzled after tonight

FC: 13.5
CC: 0
pH: 7.5
CYA: 100
TA: 100
CH: 500

Additional info:
Weather temp in Norcal has been 30-50 degrees F. Water temp hovering in high 40s.
I know my CYA is high, inherited from previous home owner using tri-chlor tabs. Have been waiting for a weather forecast of 3-5 days of rain before draining to lessen our water usage footprint while also keeping the plaster damp throughout the process.

If it was an early algae bloom and I'm breaking it up with a brush, wouldn't it be expected to see my CC rise? I never went into SLAM mode, but wondering if it was an algae problem, how likely it'd be to combat an early bloom with proper water chemistry and rigorous brushing? If I do need to SLAM It would be sometime next week when the weather shows a few days of rain and I can partially drain and re-fill the pool so I don't need such a high FC level throughout the process

Thanks!
 

cowboycasey

Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
5,256
Southern OK
Do you have Abalone shells in your pool, if so they may be your source of black spots.. From your tests it looks like you do not have any greenies growing in there.. :)
 

CrystalRiver

Well-known member
Jun 19, 2020
447
Massachusetts
I'm not convinced you have black algae. Your most recent water test was acceptable and you say you've been maintaining the chemistry. Do an OCLT to be sure. Don't just blindly SLAM.

Algae often does not produce CCs. I had a swamp, four years neglected, thick algae, backswimmers, bloodworms, tadpoles and their three parents. Never had CCs above 0.5. Having high CCs means you have nasties in the water, but not having CCs doesn't mean anything.
 

Trevor916

Member
Sep 15, 2020
12
Roseville, CA
I'm not convinced you have black algae. Your most recent water test was acceptable and you say you've been maintaining the chemistry. Do an OCLT to be sure. Don't just blindly SLAM.

Algae often does not produce CCs. I had a swamp, four years neglected, thick algae, backswimmers, bloodworms, tadpoles and their three parents. Never had CCs above 0.5. Having high CCs means you have nasties in the water, but not having CCs doesn't mean anything.

Thanks! The spots, or what could have been stains, have steadily been going away with the reestablished rigorous brushing routine. I will admit however my CYA was higher than originally thought. I know that anything above ~100 is questionable results, however I have tested multiple times and have come to the conclusion i was basically at 100 for my CYA. Today I finally got around to draining/re-filling the pool - Based of my assumptions from previous tests my guestimate was 1/2 of the water. After refilling and testing here were my results;

FC :6.5 (down from 13)
CC: 0
pH: 7.6 ( same)
CYA 70 (down from 100 - supposedly)
TA: 60 (down from 100)
CH: 300 (down from 500)

Would seem my CYA was much higher than anticipated after the drain, in the ball park of 140+

That being said - I think I'm on ta path to getting things in order, but would appear my water chemistry wasn't as good as I thought it was
 

Trevor916

Member
Sep 15, 2020
12
Roseville, CA
Do you have Abalone shells in your pool, if so they may be your source of black spots.. From your tests it looks like you do not have any greenies growing in there.. :)

No Abalone - Although we did have 50+ mph winds the last day. Woke up to find one of our patio chais in the deep end. That was fun swimming trip :)
 

Trevor916

Member
Sep 15, 2020
12
Roseville, CA
Was planning on completing OCLT this morning as recommended but didn't have a chance to test the water before work. Tested when I got home (no chlorine additions since we did our partial drain and FC was 6.0 -down from 6.5, over a 20 hour period). I think it's safe to assume we don't have the problem I was fearing *knock on wood*. 1st time pool owner OCD neurotic behavior at it's finest!
 
Thread Status
Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.