New liner bleaching around main drain

cbradfly

Member
Jun 27, 2019
7
GA
Hi All,
I had a new liner installed in April and I am already seeing some bleaching around my main drain. Does anyone have any experience with this? I am using chlorine tabs and have kept it on the low side all season. Have only shocked the pool a couple of times this year and have always brushed and ran the cleaner afterwards. The problem seems concentrated around the drain so I am wondering if there is a plumbing issue?
 

woodyp

Mod Squad
TFP Expert
LifeTime Supporter
Apr 17, 2010
10,690
East Texas
Welcome to the forum. Can you provide us with a full set of reliable chemical tests? Your ph interests me.
 

Donldson

TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
3,969
NW Ohio
Welcome to TFP! :wave:

Three questions: How many gallons is your pool? When you shock what kind specifically do you use? And how much do you use?
 

cbradfly

Member
Jun 27, 2019
7
GA
The pool is 16x30 about 21000 gallons. I have only shocked the pool about 3 times since opening. I have used Leslie's #73 shock. One bag a couple of times and 2 bags earlier this week. I started noticing in the problem about 3 weeks ago.
 

Teald024

TFP Guide
Hello and Welcome to TFP!!

Based on your info, I’d say the #73 (calcium hypochlorite) pool shock is not dissolving fully and sitting on the liner and bleaching it. Cal-Hypo is slow to dissolve. Brushing helps and that has probably saved the other parts of the liner. The main drain is in the deepest part and the Cal-Hypo sits there. The area right on the floor near the main drain sees very low flow compared to other areas above the main drain.
 

cbradfly

Member
Jun 27, 2019
7
GA
Thanks but I have been dissolving it in water before adding to the pool. Also, I took some plastic down to the main drain for a test and the suction is pretty strong so I think the flow there is good. Too good maybe?
 

IceShadow

Gold Supporter
Jun 8, 2019
1,072
Milwaukee, WI
Either way - this forum doesn't recommend "shocking" the pool with extremely high levels of FC. Instead, we advocate keeping a FC level that, while higher than what the industry recommends, accounts for the FC / CYA relationship that the industry ignores. If there's an issue with algae, cloudiness, overnight chlorine loss, etc., we advocate maintaining a higher FC level (that likely is still lower than what most people do when they "shock" a pool) until the issue is resolved.

I would recommend poking around at the Pool School articles and the forum here. Maybe this style of chemical management is for you? If so, it may help prevent future bleaching of the liner. :)
 

Teald024

TFP Guide
Thanks but I have been dissolving it in water before adding to the pool. Also, I took some plastic down to the main drain for a test and the suction is pretty strong so I think the flow there is good. Too good maybe?
Even if the drain has great flow, the flow profile around the drain still allows stuff to settle on the floor near the drain and not get sucked in immediately. The drain sucks more from above than it does from the side. And small bits of Cal-Hypo that doesn’t dissolve can sit there for a while. Especially if the bits are brushed there or slide down the slope instead of falling from above.
 

JamesW

TFP Expert
Mar 2, 2011
17,330
Suction drops off exponentially as you move away from the main drain.

Even a few inches away has almost no effect on granules on the floor around the main drain.

I would suspect that the tabs might be responsible for the bleaching if the pump is off while the tabs are in a feeder after the pump or in a skimmer where the main drain ties in.
 

DoubleEcho

Bronze Supporter
May 22, 2019
102
Pennsylvania
You're using chlorine tabs, where are you putting those tabs? Keep in mind that chlorine tabs have stabilizer in them usually and this will increase your CYA. I stay away from the tabs myself and stick to liquid chlorine.
 

cbradfly

Member
Jun 27, 2019
7
GA
Suction drops off exponentially as you move away from the main drain.

Even a few inches away has almost no effect on granules on the floor around the main drain.

I would suspect that the tabs might be responsible for the bleaching if the pump is off while the tabs are in a feeder after the pump or in a skimmer where the main drain ties in.
How does the skimmer tie into the main drain? In the past I have put the tabs in a floater but the guys who installed the liner said the skimmer was fine. I think I will go back to the floater.
 

borjis

LifeTime Supporter
Aug 19, 2014
3,068
Pacific NW
How does the skimmer tie into the main drain? In the past I have put the tabs in a floater but the guys who installed the liner said the skimmer was fine. I think I will go back to the floater.
In some setups, the skimmer has two holes at the bottom. one goes to the main drain, the other is the pump then a mechanism where you can open or close the main drain.

It's never a good idea to put pucks in the skimmer. WAY more so with vinyl.
When the pump is off, a high concentration of FC forms in the skimmer.
Someone posted a photo a year ago of their liner getting brittle and cracking at the skimmer opening.
He had kept the pucks in the skimmer.
 

JamesW

TFP Expert
Mar 2, 2011
17,330
If the main drain ties into the bottom of the skimmer and the pump is off, the chlorine tabs continue to dissolve and the concentrated chlorine goes down the pipe and out of the drain.

If you get a garden hose and stick it in one of the holes at the bottom of the skimmer, you should be able to see if water comes out of the main drain.

How many suction pipes do you have at the pump?

In my opinion, if you're using tabs, the pump should run continuously while the tabs are in the pool or system.
 
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