Black Algae Identification and Treatment

[mmanchester81]

I'm in the Houston area and in the weeks following the hurricane, I noticed an outbreak of what I believe is black algae. The water was perfectly clear and looked great but there seemed to be random spots I don't ever recall seeing before around the pool. I immediately cleaned my catridge filter and raised the FC to 20 ppm, which I tried my best to keep at for the next few days. I brushed the spots I thought were black algae with a black algae brush twice a day and it looks like they're gone now. I did an OCLT test last night and passed the test (went from 12 ppm to 11 ppm). Since the OCLT passed, I'm back to running the pool on the normal schedule; however, when I walk around the pool and look at the surface I still feel like there's black algae present. At this point, I'm wondering if I just haven't shocked the pool to a FC level high enough/long enough or if my eyes are just imaging black algae everywhere (I love my pool and this has caused me to lose a lot of sleep). I have a darker blue pebbletec surface with some small black dots as a part of the texture, so I'm not sure if I'm just over analyzing every little spot in the pool. Could someone help answer the following.

1. The best way to identify what spots are black algae? I've read articles about rubbing a trichlor tablet on the spot and if its black algae it will come off. Do you guys agree with this method or is there a better way to identify it?
2. If I was able to pass the OCLT last night, is there still a risk of black algae? I was under the impression that the OCLT would reveal whether the FC is being eaten up by any organic material.
3. Is there a risk of harming the pool surface at all with the black algae brush? I'm concerned going through and brushing such a large portion of the surface vigorously is going to end up ruining the pebbletec.
4. I bought some Algatec online to possibly help with the fight against the black algae. Based on what I've read, it can kill the black algae without a high FC level and is not copper based so won't result in any staining. Are you guys familiar with this product and what are your thoughts?

Any help is appreciated. I feel like I'm fighting a losing battle and should just stop scrutinizing every part of the pool.

 

[duraleigh]

Use a stainless steel brush daily on the black spots. Use judgement and you will have NO damage to your surface.

Keep your chlorine elevated to about twice daily. That should do it.

Got any pics? That would be helpful.

So a stainless steel brush and elevated chlorine is all you need. Passing the OCLT is not a good enough indicator.

 

[domct203]

Dave's advise is spot on.

The black algae will develop a robust biofilm, or skin, that will protect it from exposure to chlorine, hence the low CC's and passing an OCLT. This is what makes brushing the black algae so important.... you need to break that biofilm to expose the algae cells to the chlorine.

 

[HiddenRiver]

We fought black algae this past spring. There is a very good paper on how to get rid of black algae on the TFP website, I recommend reading it. It helped for us to add lots of chlorine immediately after brushing and keeping chlorine high during the day as well by continuing to add more chlorine as the levels drop —don’t let FC levels go below the high levels recommended in the paper until all algae is gone. I also think posting your water chemistry results would be most helpful to the administrators who can advise you through this website!