Chlorinate while draining?

[hairlesshacker]

So, I've been trying to clean mustard(?) algae from the walls of my pool, and the chlorine hasn't been cutting it.
Found my CYA level to be about 120, so decided to drain half the water to try to get it to a more reasonable level.
Have been maintaining 20+ ppm FC, but it's not taking out the algae. And I realize with those CYA levels I either need a lot more FC, or less CYA.

So at this point I've drained about 1/2 the water. And where the water is down, I sprayed bleach on the walls etc which immediately removed the algae.
But underwater, that algae remains. I know, SLAM it once I get it refilled..

But I was thinking, while the water was low, it would take much less chlorine to make a high concentration (albeit still has the undiluted high CYA).
Does it make sense to add a ton of bleach to the 1/2 drained pool, and try to kill more of the algae before I refill it?
Problem is I can't run the filter while it's only half full...

 

[Bperry]

So, I've been trying to clean mustard(?) algae from the walls of my pool, and the chlorine hasn't been cutting it.
Found my CYA level to be about 120, so decided to drain half the water to try to get it to a more reasonable level.
Have been maintaining 20+ ppm FC, but it's not taking out the algae. And I realize with those CYA levels I either need a lot more FC, or less CYA.

So at this point I've drained about 1/2 the water. And where the water is down, I sprayed bleach on the walls etc which immediately removed the algae.
But underwater, that algae remains. I know, SLAM it once I get it refilled..

But I was thinking, while the water was low, it would take much less chlorine to make a high concentration (albeit still has the undiluted high CYA).
Does it make sense to add a ton of bleach to the 1/2 drained pool, and try to kill more of the algae before I refill it?
Problem is I can't run the filter while it's only half full...

TFP doesn’t recommend adding “ton of” anything to the water. It’s designed to only add what’s needed and not waste time and money on other stuff.

Your half full pool of water still has 120CYA or possible more if the test that provided that number was a pool store. So it’ll still take lots more chlorine to reach SLAM level. If you go over SLAM level, you risk damaging surfaces and equipment.

So just follow the process.

 

[hairlesshacker]

no, it's not a pool store test. sorry I should have been more specific. I have a "black dot" test kit. It was somewhere around 100, so I retested with 50/50 tap water and pool water, and got around 60, which I'm interpreting as 120. I say around, because there is still a lot of subjectivity to the visibility of the black dot.

OK, I shouldn't have said "ton of". Understood, don't just blindly add and hope for the best... What I meant was, is there any benefit to trying to achieve SLAM levels of FC while 1/2 the water is out? It "feels like" it may be easier to eradicate the problem while it's still half empty, and easier to get to and scrub the problem areas.

The amount of chlorine should be the about same either way, since double the CYA means double the chlorine, but it's half the volume of water.
I assume I'm probably better off to fill it back up first, so I can run my filter.

 

[duraleigh]

I understand what you are asking but I am going to change the subject for a minute.

Can you post a current set of test results? It would be too much "stabbing at a guess" if we tried to adequately advise you without them.

 

[Aaronbr]

I'm a bit new to this, but I would drain it more since SLAM process is easier at around 20 - 30 CYA, clean the newly exposed portions of the walls like you did before, bring the water that is in the pool up to mustard algae SLAM level for your 120 CYA value, then start to refill the pool while maintaining the proper CYA/SLAM FC ratio.

 

[Aaronbr]

Here is a thread on FC level to shock a mustard algae pool. It's higher than a normal SLAM level.

Chlorine/CYA Chart

EDIT: You will find a simplified and standardized version of this chart at Pool School, Chlorine / CYA Chart. Chlorine/CYA Chart by Chemgeek FC = Free Chlorine in parts-per-million (ppm) CYA = Cyanuric Acid in parts-per-million (ppm) CYA ........... Min FC3 ..... Target FC ...... Yel/Mstrd...

www.troublefreepool.com

 

[hairlesshacker]

FC 25
CC 0
PH 7.5
TA 120
CYA 120

thanks aaron, yep - I've got that one bookmarked already, along with ben's best guess chart...
I think you're right, draining more to lower more CYA is probably the best bet.

 

[reggiehammond]

Can you share some photos?

For every 100 posts about people with mustard algae, I can't really recall anyone actually having it.
Most people just have plain old algae - which the SLAM process can annihilate.

Make sure you follow the SLAM process first, before turning to the mustard algae portions.

 

[hairlesshacker]

@reggiehammond , yeah - I don't know why I said mustard. It's probably "plain old" algae. But it's on the walls, not making the water green. Or perhaps my filter keeps the water clear in spite of the bloom.

 

[DrewLG]

[Deleted] Oops, math error.