First SLAM - painted gunite pool with a little algae

[rnjw]

After a few weeks learning the ropes I think I understand the need to keep a high FC to get rid of algae.
I was pleased with an otherwise sparkling pool (new home owner, old pool) and very low chlorine making it quite comfortable. But I noticed algae growing as the chlorine was getting used up quickly. We have been at 85-90 degrees for weeks.

Using TFP, concentrated CLorox bleach (thanks Costco) and sweeping and brushing I've now managed to go from 20 CYA to none. After lowering PH to 7.5 with muriatic acid I started adding bleach going for a target near 10 FC to SLAM.


Most of the algae on the bottom and side has disappeared but a couple of stubborn stains on the bottom at the shallow end. I don't know how high to take it without causing harm.

1 gal bleach last night, this morning recorded FC 8 CC 0
Added 1/2 gal bleach and 2 hours later FC 7 CC 0

My understanding is that I should see ALL algae gone. I scrubbed with a brusch and the couple of stains remain. Should I buy, add CYA now or raise the FC up to 10 first?

 

[Casey]

If you have little to no CYA in the pool, you need to get it in there. You are losing your FC to the sun AND the organics and losing. You need to get to 30-50 ppm and (whichever you target) and SLAM the pool to that level once you drop the sock of CYA.

The algae will die, keep SLAM'ing the pool. If you stop, it will be back!

 

[Kiss4aFrog]

SLAM is not a one time thing of tossing in bleach, it's a process. If you have algae you do need to SLAM. Where is your pH at ?? If it's high or low you should adjust it before you SLAM
SLAM is MAINTAINING the proper level of chlorine in relation to your CYA and holding it up at that level until you kill ALL the algae. If you can see algae you have it but just because you don't see it does not mean you've killed it or that ALL of it is dead.
This is how it's done: http://www.troublefreepool.com/content/125-slam-shock-level-and-maintain-shocking
It isn't over until:
CC is 0.5 or lower;
You pass an OCLT (ie overnight FC loss test shows a loss of 1.0 ppm or less); and the water is clear.

When all three are true, you are done SLAMing and can allow the FC to drift down to normal levels.


Not sure how you managed to get from 20 to zero CYA or why you thought it was a good thing You should have some so the chlorine doesn't just burn off from the sun. You need to add some in a sock to your skimmer and knead that bag to get it dissolving into the pools water. You should also not backwash for a week so the CYA has a chance to get dissolved from the filter into the water.



- - - Updated - - -

I don't know how high to take it without causing harm.

http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

 

[Butterfly]

My understanding is that I should see ALL algae gone. I scrubbed with a brusch and the couple of stains remain. Should I buy, add CYA now or raise the FC up to 10 first?

Raise FC to 10 first. Then, get some CYA in there. I suggest you only add about 20ppm CYA for now, because you probably have some left still in the water that is too low to show on the test.

You will need to clean the filter when he pressure increases 25% over clean pressure psi. You will lose a little CYA, but cleaning the filter is priority.

Once the CYA is dissolved, increase SLAM FC level accordingly.

Is the entire pool painted or do you have some/any exposed plaster?

Welcome to TFP

 

[rnjw]

Thanks to everyone responding so quickly with so much useful help..

Raise FC to 10 first. Then, get some CYA in there. I suggest you only add about 20ppm CYA for now, because you probably have some left still in the water that is too low to show on the test.
--- agree that the t-1000 test cannot measure below 20.

You will need to clean the filter when he pressure increases 25% over clean pressure psi. You will lose a little CYA, but cleaning the filter is priority.

Once the CYA is dissolved, increase SLAM FC level accordingly.

Is the entire pool painted or do you have some/any exposed plaster?

Welcome to TFP

-----------------
Starting at a PH 7.5 and CL 5 I added about 2lbs of CYA last night. Had the filter running overnight at low speed.
This morning's readings are:

CL 4 CC 0 PH 7.5 CYA now 45 TA 100

Guess I will have to restart the SLAM unless the stubborn stains at the shallow end are not algae. They do not disappear even with aggressive brushing.



The filter is running at 15psi which is the level I started with. (The developers who prepared the house and pool for sale did not leave me any information. They painted all of the pool including the tile rows at the top. Pump and filter are fairly new.)

 

[tim5055]

What are you testing with?

If you don't already have one, you will need to pick up one of the recommended test kits. To effectively practice the TFPC methods, the FAS/DPD chlorine test is essential. All the kits on the list contain that test while very few other kits do. The kits sold at the pool store generally won't won't cut it, but be careful pool store employees are known to say “it's the same thing”. Generally it's not!

If you are testing CYA with test strips your numbers can be all over the place as they are not accurate. You say you started 20, went to 0 then 45 the morning after you added CYA. Unless you are sure of the 45 with a test kit based on Taylor chemicals/reagents I would stop adding CYA until you know where you are.

 

[rnjw]

I am using a T-1000 kit and the basic K-1000.
Just retested after 3 hours and the CL is still showing 5-10 for the basic test with a PH 7.5
FC is 3 on the more accurate cylinder test. Why such a difference?

CC is still 0

CYA reads 55 without swirling, 45 after swirl. Is this a normal test variance or a reliable change?

BTW, the yellow algae is gone and I don't know what is the substance of the stains.