High TC but green algae still appearing

[Jimh64]

Hi everyone, thanks to all of you, my water is great. However I am trying to help a friend. She has a 10000 Gallon Vinyl Pool. She has green algae on the sides of her pool and a little on the bottom.

I tested her pool and her levels are:
FC 16
CC 1
TC 17
T/A 180

With her FC at 16, I wouldn't think she should have any algae, becuase it has maintained that level for over 2 days.

Any suggestions?

Thanks!

 

[Smykowski]

Shock level is dependent on CYA level. Can you post a full set of results?

 

[Jimh64]

Shock level is dependent on CYA level. Can you post a full set of results?

I knew I forgot something! I will get the CYA Level tonight...

Thanks!

 

[Jimh64]

Ok, here are the reults:
FC 20
CC 0
TC 20
PH 7.5
T/A 170
CYA 120

In checking the Pool Calculator, it looks like the best thing is to drain and refill about 60% of the water. Shock level would need to be 28!

What do you think?

Thanks!

 

[jblizzle]

The CYA could be well above 120ppm so changing even more water out may be needed.

But, you do understand why the pool is green. With the high CYA, FC likely dropped too low at some point and now the FC is still well under the shock level.

How are they chlorinating?

Posted with Tapatalk ... sorry if I sound short ... hate typing on phone

 

[Jimh64]

Thanks for the reply. Yes, I agree, I told her it is too high and that she needs to drain the pool. She is using granular chlorine and shocks every 2 weeks! I told her to start using this forum and to switch over to Bleach..

In the meantime, if she adds bleach to get up to a shock level, will it decrease her cya, or is draining the only way to do that?

 

[jblizzle]

PARTIAL drains are you only option to lower CYA. Fully draining could ruin the liner.

No point in adding any chems until you get the CYA down.

Likely the granular chlorine AND the shock were raising the CYA. Maybe you should re-do the CYA test with a 50/50 mix of pool and tap water to start and then double the result to see how high it REALLY is.

I would not want them to replace 50% of the water and then you retest and they are mad at you that the CYA is still over 100 ... better to have full disclosure to start that multiple water replacements may be required.

 

[Jimh64]

That sounds like a great idea!

I will test using the 50/50 method.

 

[Qwaxalot]

You're on the right track, reduce the stabilizer level, brush the algae, and the chlorine will solve the problem.

 

[UnderWaterVanya]

Ok, here are the reults:
FC 20
CC 0
TC 20
PH 7.5
T/A 170
CYA 120

So you can have active growing algae and still get a CC of 0? Wow... I didn't know that. I'm new to this and still learning but that was a shock.

 

[linen]

So you can have active growing algae and still get a CC of 0?

Yes, that is part of the reason there are three criteria in the shocking process (see my sig), any one of them is an indication of organics.

 

[UnderWaterVanya]

So you can have active growing algae and still get a CC of 0?

Yes, that is part of the reason there are three criteria in the shocking process (see my sig), any one of them is an indication of organics.

Understood. I'll hopefully get to the OCLT tonight. The water is looking great. I ran it up to about 15ppm (again no time to validate the exact value after adding bleach) and this afternoon on a hot sunny day it was only down to 12ppm so I am hopeful.