# Calculating shock level - conflicting chart / calculator?

#### Steverino

Hi all,

Opened our pool last weekend & found very green walls & floor, but fairly clear 54 degree water. Usually when I close I throw in the floater with chlorine pucks, but last fall I tried Polyquat instead. Maybe a bad move... in the past I've never had much algae on opening.

Anyway, I got the pump fired up, walls & floor brushed, and began SLAM with 10% Walmart bleach. My CYA was/is about 50, and I figured I shouldn't bring it up to SWG level until the SLAM is done. So the Pool Calculator says with CYA at 50, shock level should be 16. However the Pool School Chlorine/CYA Chart shows a shock of 20 for CYA of 50 (non-SWG; the SWG chart doesn't go down to 50).

My question is - should I be trusting the Pool Calculator shock of 16 for my circumstances? Or do I need to go higher?

The pool is looking really good, and I did pass OCLT Thursday morning but ran SLAM one more day for good measure and failed it this morning... So that made me question my process a bit.

Any thoughts appreciated... Thanks!

#### tim5055

TFP Expert
Hi all,

Opened our pool last weekend & found very green walls & floor, but fairly clear 54 degree water. Usually when I close I throw in the floater with chlorine pucks, but last fall I tried Polyquat instead. Maybe a bad move... in the past I've never had much algae on opening.

Anyway, I got the pump fired up, walls & floor brushed, and began SLAM with 10% Walmart bleach. My CYA was/is about 50, and I figured I shouldn't bring it up to SWG level until the SLAM is done. So the Pool Calculator says with CYA at 50, shock level should be 16. However the Pool School Chlorine/CYA Chart shows a shock of 20 for CYA of 50 (non-SWG; the SWG chart doesn't go down to 50).

My question is - should I be trusting the Pool Calculator shock of 16 for my circumstances? Or do I need to go higher?

The pool is looking really good, and I did pass OCLT Thursday morning but ran SLAM one more day for good measure and failed it this morning... So that made me question my process a bit.

Any thoughts appreciated... Thanks!
First, you are correct - do not make any upward CYA adjustments until the is over.

Use the [FC/CYA][/FC/CYA] for calculations. For now the SWG section is not applicable as you are manually chlorinating the pool.

When you say Pool Calculator, are you using our or the old calculator named Pool Calculator (not controlled by TFP)?

#### Jezza

TFP Guide
That's right. You need to use 20FC for a CYA of 50 to SLAM.
Not sure if you have done it yet but it is best to turn off the SWG for a SLAM and it absolutely must be off to successfully conduct an OCLT.