It might be Algae

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M

Mypool12

0
May 20, 2017
46
Central New Jersey
Pool Size
25000
Surface
Vinyl
Chlorine
Liquid Chlorine
I had a yellowish substance on my top step about a week ago. At the same time, I started losing chlorine. I decided to slam the pool. I got the chlorine levels up to 18.2 and tried to maintain them at that level for a few days. The pool has always been clear, I passed the overnight test 2 days in a row and so I let the chlorine levels come back down. The chlorine levels went from 18 to 17 on the second successful over night test. The next night it was it was at 14 and I decided to not test early the next morning but tested later in the day on the following day and got a reading of 7.5. Today, I got a reading of 0. I am not sure if I have algae or something else. From what I have read online, yellow algae should brush off quite easily. This yellow substance required to be scrubbed off with a wire brush.

Any help would be appreciated. I have my readings below and then the results from the 2 different pool stores.

My current readings right now are as follows:
FC 0
CC .2
pH 7.2
Alk 60
CYA is 30
CH is 160

I went to 2 different pool stores to see if they had any ideas and to check my numbers against their figures.
First store
FC 0.05
CC .08
pH 7.5
Alk 48
CYA is 48
CH is 142

2nd store
FC 0.4
CC .0
pH 7.2
Alk 78 (adjusted alkalinity 48)
CYA is 100
CH is 262

They thought the yellow substance might be pollen or my inability to hold chlorine is from fertilizer that was applied by a farm near by.
 
Did you add chlorine every day after your SLAM to maintain target level FC based on [FC/CYA][/FC/CYA]?

- - - Updated - - -

Also - from the results you posted from the two pool stores, reinforces why we do not trust their testing --
 
Yes. I added chlorine multiple times each day to maintain a high FC level. The FC certainly would have dipped below 18 during the day but that level needed to be maintained if I have yellow mustard algae. I not sure if I did or not.

What do you suggest that I do?
 
Did you continue to add chlorine every day after the SLAM was over to maintain your target FC?
 
Yes. Yesterday my chlorine level was at 7.5 and this morning it was 0. I was expecting a 3-4 range and was going to bring it up to 4.5. I was surprised with the 0 reading.

I forgot to mention that the pool store said my phosphates were at 438.
 
OK. Get your FC back to target level. See if your FC loss is normal or not.

Phosphates are not material if you eliminate the algae.
 
Target level based on [FC/CYA][/FC/CYA]. Use the upper end of the range, or 6 ppm FC.

Based on your last reported CYA of 30 ppm.

You may find raising that to 40 or 50 ppm will help.
 

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OK. My heater manual said to not maintain a FC level above 5 ppm. That is why I was trying to maintain a FC of 4.5. Should I check it again this evening or should I check it in the morning?

Thank you for your help.
 
That level of FC is assuming 0 CYA. The active chlorine with your CYA in the water is a tiny fraction of 5 ppm FC in 0 CYA.

There is no need to limit FC as long as you are using the [FC/CYA][/FC/CYA].
 
That is not an unreasonable drop during the day.

I suggest you raise it to 6 ppm, let your pump circulate 30 minutes, test FC, record it, then in the morning, test the FC after letting the pump run for at least 30 minutes. See if you pass the OCLT.
 
Last night @ 9:30, I tested the FC and recorded 6.5 ppm. I tested the FC again this morning @ 6:30 and recorded 5 ppm. I will bring the chlorine back up to 6 ppm. Do you propose I do anything else at this time. Thank you for your help.
 
A drop of 1.5 ppm FC overnight is problematic. I know you have just finished a SLAM but I would suggest going back to it.

Run a full suite of tests before you raise your FC to SLAM. Be diligent about the CYA test and be sure to round up any number you get. I suggest doing the test a number of times, with the same sample, by pouring the sample back into the mixing bottle each time after reading the value. Then take those results, average them, and round up to the nearest whole 10. Use that for CYA.
 
Hooray!! After two days of slamming, I think I am in the clear. Last night I tested my FC at 11:30 pm and recorded 17.5. This morning at 6:00 am, I recorded my FC at least at 16.5 but less than 17. My CC was less than .5. My pool has been and is still crystal clear.

Do I just let the chlorine drift back down to FC of 6 ppm? Is there anything else that I need to do?

Thank you for all of your help.
 
You may find it helpful to add 10 ppm of CYA powder. Then stay at the top of the target level for FC based on [FC/CYA][/FC/CYA]
 

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