water clear, but black algae keeps coming back

[mxfan]

Hello everyone!

I have been reading a lot on this site in the last few months and appreciate all the useful information. I have have an issue with a green pool and have also had black algae off and on again for the last few months.

I have through reading this site been able to manage and temporarily get rid of the black algae and it has been basically not existant for about a month now.

I test the water morning and night (no less than once a day) and keep the fc level no lower than 3 ppm. I have a target of 5-7 ppm that I normally keep it at. It never holds chlorine (which my pool service guy says it will eventually) but from reading info here I realize that it is not uncommon for it to lose some due to sunlight. Last week I was adding the lowest amount I have in months and it was only losing approx. 1 to 1 1/2 ppm daily. I thought this was pretty good. My pool service also have been using chlorine tabs in the skimmers and I think that helped to maintain the levels.

As of Friday everything was looking good. Then by Saturday I started to notice a major loss of fc. 4-7 ppm. I raised the fc level to 16 ppm and overnight it lossed 8 ppm? At this point (Saturday) I found a small area that had the black algae appearing, but thought that maybe it had been there the whole time and that I hadn't noticed it.

I shocked it today (Sunday am) and raised it to 16 ppm. By 6 pm it was back down to 8 ppm. I raised it back up to 16 ppm by adding bleach.
By early evening, I started to look closely and everywhere I look the black algae is coming back...

I am wondering how in one day the black algae can start to come back even with the fc levels not falling below 3 ppm?
Should I keep it from going below 5-6 ppm instead?

I am so tired of shocking and not being able to enjoy the pool, and to go through it all again 2-3 weeks later when I think I have it under control-help...

water is still clear and looks good

Current test results:
fc 8 (prior to shocking)
tc 8
ta 120
calc. hard. 220
ph 7.8
cya 35 (read 40 last week)

temp. 84-86

Thanks for your time!
...Eric

 

[Guest]

I am wondering how in one day the black algae can start to come back even with the fc levels not falling below 3 ppm?
Should I keep it from going below 5-6 ppm instead?



cya 35 (read 40 last week)

temp. 84-86

Thanks for your time!
...Eric

First of all, understand that black algae only happens from improper pool maintenance over a period of usually weeks. It does not happen quickly. It means you have not maintained your water chemistry properly. (I am not blaming you here. Just trying to make sure you understand that you need to reevaluate your pool maintenance procedures)


With a CYA of 30-50 3 ppm is the MINIMUM you should ever let your FC drop and 4 is recommened. If you hare having problems then by all means keep the FC a bit higher, say 4-5 ppm!!.
Black algae only happens when there is a too low chlorine condition OVER A PERIOD OF TIME which means you have been letting your FC get to low and leaving it there. Bumping the chlorine high and then letting it drop before adding more will not keep black aglae away. You need to maintain constant FC levels. Kill the algae then keep the FC a bit higher. I suspect that you originally did not have enough CYA in the water and there was a lot of chlorine loss from sunlight. The tabs your service put in the skimmer has bumped up your CYA. If you had a pool service and you got black algae and they were responsible for making sure that your water was balanced and chems were at appropriate levels then they just did NOT do their job! (Imagine that, a pool service that did not do their job properly! --sarcasm intended! :lol: :lol: )

 

[frustratedpoolmom]

Black algae is a pain in the rear. Sorry for your troubles I can totally understand your frustration.

Black Algae is resistant to chlorine. It's sort of got this tough outer shell, that you have to destroy so that the chlorine can get to the insides and kill it. So with Black Algae, constant brushing with high FC is the key.

I would shock this evening, get an old suit, get in, and brush brush brush. Then shock again tomorrow, repeat the brushing. Repeat this process as necessary, till your FC holds overnight. Then run with the the 7 FC for a while, but keep on brushing every day. I suspect it wasn't completely dead the first time, just lurking there, waiting for the ideal conditions, a FC level that it could survive in. Add enough bleach each day night so that the FC stays around 7. Good luck. :-D

Are you certain about your CYA level? Here's a link with pictures, to ensure your are doing it correctly. If your CYA is higher than you think because of the tabs, your FC could be too low? Just guessing here.

 

[mxfan]

Thank you both for your replies!

I will bump up my low level fc to 4-5 and keep an eye on it. Normally it is at about 6-7 ppm and I add bleach to it when it gets down to about 4...but there were a few days last week that it got down to 3 but no lower?

cya is at 35, and I use a Taylor 2006 kit to test my water (I purchased the Taylor before I was a member here) but it seems to be a good kit according to what I have read here. Thanks for the link so I could verify that I was reading it correctly.

I will start the routine of brushing and keep the fc at shock level.

The bummer part is that this is only our second year of having our pool and it is a natural rock style (sculpted cement) which looks really nice...but the pebbletec is only on the very bottom of the pool and the walls are the natural rock look which has a ton of texture and nooks and crannies. It is about a 3-4 hour deal to brush the walls

At this point it just seems like a never ending battle, and I actually am in the pool to 'fix' it then to enjoy it.

Again I appreciate all your help and comments.

Thanks.
...Eric