Green on pool walls

[HiddenRiver]

Things have been going well with our pool this year. The past two weeks we have had more than 8 inches of rain. Needless to say though I have been keeping the FC up as best I can, today I noticed green on the walls of the pool, but is it possible that it isn’t algae? The water is crystal clear and the water chemistry results were as follows:

FC 7.5
CC 0
TA 70
CH 175
CYA just less than 30, does that make it 20?
pH 7.6

CH used to be 250 but rain I guess lowered it. Pool math says I need to add CaCl and Borax. But if this is algae where is the CC? Pool math said the CSI was -4.0. I don’t understand the relationships.

 

[woodyp]

We always round up CYA, so call it 30. Performing an OCLT will determine if that's algae----which it probably is. Overnight Chlorine Loss Test You can have algae without having any CC btw.

 

[Richard320]

If it feels slimy, it's algae. If it brushes off, it's almost certainly algae.

An overnight loss test will confirm it, but why wait and let it get out of control if it is algae? Hit it hard with chlorine and brush 'til your arms can take no more. Run theOvernight Chlorine Loss Test tonight.

You're in the enviable position of being able to use Cal-hypo to chlorinate for a while. Your pool is huge, so you can use pounds and pounds of the stuff without driving CH too high. Like fifty pounds of 73%!!!

I plugged your numbers into poolmath and I don't see how you got CSI of -4. I don't know your exact temperature, but if it's around 80, your CSI is fine,. Try it again and be sure to press enter a lot so it updates.

 

[duraleigh]

but is it possible that it isn’t algae?

I can't think of anything that would show up green in your pool that isn't algae. Time to read the SLAM article and SLAM your pool. You will likely need to brush frequently during SLAM.

CSI will never be an issue in your pool......I would ignore it.

CC is an indicator of organics in your pool. It is not a guarantee they are there. Don't be surprised if CC's start to show up when you begin the SLAM.

 

[HiddenRiver]

We always round up CYA, so call it 30. Performing an OCLT will determine if that's algae----which it probably is. Overnight Chlorine Loss Test You can have algae without having any CC btw.

I did not know this...

 

[HiddenRiver]

Thanks folks! A SLAM is in my future tonight. I do have some cal-hypo. What would magnesium chloride do?

 

[mknauss]

Magnesium chloride is a salt. It is not recommended to be used in pools.

- - - Updated - - -

Why are you waiting until tonight to start the SLAM?

Time is of the essence ----

 

[woodyp]

Starting the SLAM now won't keep you out of the pool today if that's what you're thinking.

 

[HiddenRiver]

I brushed the walls and added four bags of cal hypo at about 2:00. I don’t know if this is enough. FC was at 20 at about 3:00 but I don’t think it was all dissolved. We swam in the pool.