Algaecide to winterize vinyl in-ground pool?

maintainpool

Well-known member
Apr 30, 2018
82
Orange County, NY
We just had a new vinyl liner installed this season. The pool gets closed/winterized tomorrow, we have a Loop-loc mesh cover. The pool water temperature is still in the mid-upper 70s, outside air temperature is in the 70s - 80s during the day and 50s - 60s during night.
We use liquid chlorine for a sanitizer (the BBB method).

Current water specs are: TA=110, PH=7.5, Calcium Hardness=300, CYA=35, FC=14 (just shocked the pool), Water temp=75 degrees

Should an algaecide be used right before putting the cover on the pool? is so, which type? some have copper and others have poly.

How is this copper based one? Super Algaecide - 7.1% Copper Pool Algaecide - In The Swim
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,230
NW Ohio
Don't use copper based algaecide. Ever.

Adding algaecide at closing is optional. Some swear by it, I personally don't use it. Results for both options seem pretty much the same: hit and miss. With a mesh cover you might as well. If you choose to use algaecide use a 60% polyquat.

Are you following TFPC? Your comment about shocking the pool is concerning. Were you implementing the SLAM Process, or just raising your FC? If the latter, then why?
 

maintainpool

Well-known member
Apr 30, 2018
82
Orange County, NY
The FC was raised to shock level because a small amount of green algae was growing on the pool walls in deep end.
Should the pool be closed at shock level or a higher than normal FC level?

Don't use copper based algaecide. Ever.

Adding algaecide at closing is optional. Some swear by it, I personally don't use it. Results for both options seem pretty much the same: hit and miss. With a mesh cover you might as well. If you choose to use algaecide use a 60% polyquat.

Are you following TFPC? Your comment about shocking the pool is concerning. Were you implementing the SLAM Process, or just raising your FC? If the latter, then why?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
16,299
Northern NJ
CYA=35, FC=14 (just shocked the pool), Water temp=75 degrees
You can’t measure CYA 35 and you cant interpolate the FC/CYA Chart. If the dot disappears between 40 and 30 then you round up and call it 40. Your SLAM FC target is then 16.

The CYA scale is logarithmic, not linear and halfway between lines is not 5. You cannot eyeball what 5 is.

You need to use the correct SLAM FC level to successfully clear algae.
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,230
NW Ohio
If you have algae then you need to follow the complete SLAM Process, not just raise the FC temporarily. If you can see algae that means there is a lot more in the water that you can't see and it needs taken care of.

If you are using Polyquat then you can close anywhere between minimum and SLAM FC level. If you are not then you want to close at SLAM level.

Have you had a chance to read the Closing an Inground Pool article?
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,230
NW Ohio
No. The active chlorine at SLAM level is actually quite low. My liner is well over 10 years old and I close at SLAM level and open to readable chlorine, so it is likely being exposed to SLAM level for weeks if not months.