Possible black algae, not positive though....help!

[CajunGuy]

The other day when cleaning my pool on the deep end, I noticed some spots in the deep end of my pool (gunite). Mostly following the pattern along the bottom edge where dirt and some debris tends to accumulate. Although it doesn't accumulate often because I'm anal about keeping my pool clean. Anyways, I decided to put on some goggles and swim down there to get a closer look. When I did, I noticed it was more spots than I thought. Now here's the thing, they look dark green to me, not actually black. So I'm not sure if this is black algae, but I just assumed so. I got a very stiff bristled grout brush and went to work scrubbing all the little spots on the deep end. It took a good bit of elbow grease and scrubbing to get the majority of the spots off and figured bleach would kill the rest.

Fast forward a few days later, I got back in the pool and noticed the spots were there again...ughhhh! Anyways, I scrubbed them again as best I could (not easy to do in the deep end when you have to continuously come up for oxygen lol). I shocked the pool after this again, but with triple the dose. It was getting late/dark to get a full set of results, so I figured I'd just dump 3 gallons of 10% bleach in there (should bring my FC to around 15ish). I will try to get a full set of results this afternoon when I get home. I plan on going buy a stainless steel brush today after work and use that instead.

My questions are:

1. Does this sound like black algae?
2. Is there anything else that I could put in there afterwards (like a black algaecide) to help prevent it from coming back since I've read that black algae is a curse and it never really goes away because it's still in the pores of the plaster?

It's kind of freaking me out, just the thought of it possibly always returning. But then again, I'm not even sure if it is indeed black algae. Most of the spots I saw were about a pencil eraser in size or a little smaller. Any other advice besides SLAMing and brushing vigorously?

 

[kimkats]

Get some with your finger nail and bring it up. Wipe it on a white paper towel.....it should be green when you do this if it is algae.

Kim

 

[CajunGuy]

Get some with your finger nail and bring it up. Wipe it on a white paper towel.....it should be green when you do this if it is algae.

Kim

Ok, I'll do that this evening when I get home from work. What else could it be if it's not algae? For me to be able to scrub it only to have it come back a few days later? How do I know if it's actually "black algae" as opposed to green?

 

[AftonJeeper]

How do I know if it's actually "black algae" as opposed to green?

Taste. Black algae tastes burnt. J/K

Do an OCLT test.

 

[CajunGuy]

Taste. Black algae tastes burnt. J/K

Do an OCLT test.

How would an OCLT determine what type of algae it is? I plan on doing one anyways, but correct me if I'm wrong...all that would tell me is if there is some sort of organic matter (algae) consuming my FC, not actually what type it is?

 

[kimkats]

Here is the TFP link for black algae:

Pool School - Black Algae

The OCLT will not tell you what algae you have. It just tells you that something is eating your FC.

Make sure to read the link above. Note the last part about your FC level once you think it is all gone.

Kim

 

[kadavis]

Try rubbing a chlorine tablet right on the spots, whether it's green or black algae it will kill it. Black algae is really a dark blue green algae with a protective cover over it

 

[CajunGuy]

Update:

Well after dumping 3 gallons of 10% bleach day before yesterday (also set my SWG to 100% and my salt is perfect at 3500) and scrubbing like a mad man, I came back yesterday evening and had a look around the bottom and I didn't see any new spots. I shocked it again (FC was way up around 15) and scrubbed again even though I didn't see anything.

Question now:

I read somewhere that the "black algae" usually takes a long time to form from a neglected pool. I keep up with mine religiously (pretty much daily lol) and can tell you that these algae spots were only 1-2 days old when I noticed them. Is there any chance that these spots could have been regular old green algae instead? I was just always under the assumption that green algae wouldn't actually form spots like that and instead would just turn the water a greenish tint.

 

[AftonJeeper]

With a SWG your shock level is 24 at a minimum, your CYA should be at 60 for that level. Ideally it would be 70 or 80 witch would be an even higher shock level, 15 isn't high enough. Have you read the SLAM article? shock level and MAINTAIN. That is the best way to beat any algae outbreak.

Did you pass the 3 criteria to end a SLAM? OCLT, Clear water, and CC under .5

Yes there is a chance it was regular algae and there is a chance it could come back.

Hopefully tropical storm Cindy doesn't cause you any more problems.

 

[CajunGuy]

With a SWG your shock level is 24 at a minimum, your CYA should be at 60 for that level. Ideally it would be 70 or 80 witch would be an even higher shock level, 15 isn't high enough. Have you read the SLAM article? shock level and MAINTAIN. That is the best way to beat any algae outbreak.

Did you pass the 3 criteria to end a SLAM? OCLT, Clear water, and CC under .5

Yes there is a chance it was regular algae and there is a chance it could come back.

Hopefully tropical storm Cindy doesn't cause you any more problems.

Well that's the thing...I recently had to drain a few inches off my pool several times due to rain and it ended up lowering my CYA a bit. It was at 40 when I checked (I usually try to keep it a 70). So looking at the Chlorine/CYA chart, it said shock level was 16. So that why I've been keeping it around 15-16ish.

Instead, should I bump my CYA up now to 70 and then raise my FC level to 28? Or should I just keep it where it's at?

 

[AftonJeeper]

Keep right where you are, it will help keep the chlorine expense to a minimum. Once you pass the 3 criteria I would start moving it back up around 70 and monitor the FC closely for a little while.