Need to get rid of black algae but unsure of adjusting levels before I shock

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Floridamom

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Nov 10, 2014
20
Gainesville/Florida
Hi! I'm new to TFP and have been reading for hours over the last week. I have learned so much already and wish I had found this site 7 years ago when my pool was new. I've read through Pool School so I hope I am doing this correctly so as to not make you repeat yourselves.

So, my first concern is black algae. I did the fingernail scrape, and it looks like tiny tiny black spots in the pool (shallow and deep ends) but smudges green on white paper. Over the summer we noticed them and could scrape them off with some effort. Now, months later, although they don't seem to be multiplying, they are still there. I have been a little lax about my water testing so I take the blame for this. My pool looks crystal clear but these little spots are hanging on. I'm running my pump at 60% 5 hours a day right now.

I ordered the Taylor K-2006 after reading your forum and tested the water yesterday. I had a much simpler drop test that needed replacing. I also took a sample to my local pool store, which I do not like going to other than to purchase acid and salt.
Here are the results of my test and theirs:
Taylor , Pool store
FC 6 , 7
CC none, no results shown
Ph 7.8 , 7.8
TA 60 , 80
CH 210 , 250
CYA less then 30, 20
salt SWG green, 3100

I know my CYA is low but I don't know what to do first. I want to get rid of the black algae as efficiently as possible.
Thank you for your help
 
Welcome to the forum!

Best new kind of poster, because you already have the test kit, and you've already done a ton of reading.

Basically you're goinf to follow the SLAM procedure, but in addition you'll be mechanically scrubbing the algae spots at the same time to expose them to the elevated chlorine levels.

I think there's a black algae specific article in pool school you can read if you haven't seen it already.
 
+1 what smykowski said. Ridding completely of Black algae is a process......long term and not a one-time fix

Please be sure you follow the SLAM article to a T and then be diligent about the brushing you will need to do. Don't do just "some" brushing and hope you got it.

Follow the procedures carefully so you know you got rid of it.
 
Thank you, both. I found the SLAM article and will get started in the morning. I'm assuming that I should check my numbers one more time after lowering my Ph to 7.4 before I start adding the bleach. I found the chart that Chem Geek posted that began with CYA levels of 0 since mine is at 20. Am I understanding it correctly that my shock level will be 8.3?
 
Looks like you have a good grasp of things.

Shock level for CYA 20 is FC 10 here:
http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

I see Chem Geeks chart that says 8.3 which is conflicting information but its fine to use his:
http://www.troublefreepool.com/threads/2177-Chlorine-CYA-Chart

I see you have a new SWG. They recommend to run the CYA level higher so the SWG doesnt have to work as hard if your pool is outside. Not sure about if its inside but looks like it is around the 20-30ppm CYA level for inside. I wouldnt worry about this part until your done slamming. Maybe someone will chime in here to clarify things.
 
Yes, I did install a new SWG last week after the previous one finally died but after 7 years :) My numbers were slightly out of whack with that. And, my last drop test kit didn't have a CYA test in it so I really never knew what the level was. Now that I know its 20, which is low, I wasn't sure if to shock first and then adjust it. I'm assuming its fine to move ahead and adjust it after I get rid of the algae spots.
Oh, it is an outside pool within a screen enclosure.
 
Ok, I'm in the first 3 hours of slamming. My Ph tested at 7.4 on its own this morning so I didn't need to add any m.acid. I added 54 oz of 6% regular bleach and brushed the pool. I tested the FC and CC two hours later. I started this morning at 7.5 FC and 0 CC with a CYA of 20 and was still there two hours later. So I just added another 54 oz of bleach and turned my SWG on to 80%. Is that ok? I know I need to turn off my SWG at night to get an accurate OCLT. I'm hoping it will help get the FC higher now though. Am I on a normal track? Also, other than the tiny black spots, the water has been crystal clear the entire time.
 
How did you calculate 54 oz of bleach? I think that will only raise your FC by 2 ppm.

Using the SWG during a SLAM is usually very unproductive for a newbie. You will cause less confusion if you turn off the SWG and manually dose.

You should immediately brush the black spots.......Have you done that?
 

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I used the Chlorine/CYA chart to get a shock level of 9 (one chart said 8.3, the other said 10...so I went to the middle). My CYA is 20. I used the pool calculator to get 54 oz. Am I using it incorrectly? And, yes, I have already brushed the black spots 3 times today so far with my new SS brush. I'll go turn off the SWG.
 
17,280 gallons.
36 fl oz of 6% bleach = 1ppm FC

If you put 54 fl oz of 6% bleach in there, then you raised your FC by 1.5ppm. If thats what you meant to put in there to raise it back to 9ppm, then yes you calculated correctly.
 
I dont see anything here that your missing except that you could raise the FC to 10 instead of 9.
Turn off your SWG and follow the SLAM process. Dont halfway complete the process. I see this a bunch.
Keep brushing.
 
Floridamom said:
I'm heading to the store to buy some new bleach. Something doesn't seem right. I just tested the water after adding 54 fl oz of 6% two times now and the FC is still at 7.5?!? It hasn't budged.
I'm going to town scrubbing the black spots though...
Click to expand...

The FC was used by the algae and just appeared to stay there. If you hadnt added any it would likely be close to 0ppm. Keep at it. The FC will eventually start to stay. Seems your doing a good job.
 

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