AGP opening - why shock?


This is my first opening. Peeking under the cover, the water looks clear, thankfully!

In reading here, I see that the general advice is to use chlorine shock to bring the FC level up to 3. I am probably missing something stupid, but why wouldn't I just use bleach in addition to my SWG to bring the FC level up to the appropriate level?

Thanks for illuminating me!!!


TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
NW Ohio
Where on this site did you find the suggestion to bring the FC level up to 3?

You want get your pump running and then do a full batch of tests and then adjust whatever needs adjusted. You will bring your FC level up to SLAM level unless you measure an FC level higher than the stated minimum for your CYA level.


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

I'm not sure where you found that info, but it does not sound right to me..

We generally want our members to test their water and then, based upon the results, determine what needs to be added or not.

An FC level of 3 would not at all be in the "shock" range...

The only reason that you might want to add Liquid Chlorine or Bleach to get your pool up to the desired FC level, is just because it would be quicker and take the strain off the SWCG.

Check out this chart...

If you look at the chart, you will see that you can't know what your FC should be unless you know your CYA level..

Thanks for posting,

Jim R.


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
If you have zero CYA, your FC level should be 3. With higher CYA, you need higher FC.

The problem is the use of the word "Shock." We use it as a verb, as in a wallop with bleach. Pool stores sell a product called shock. If you suffer from low CYA & high pH or low CH, you could use one of the shock products (note there is no standard definition as to which chemical is actually shock!) to raise the FC to shock level, but then you're juggling multiple parameters. Bleach is simpler than "shock" products and all you're adding is chlorine and a little salt.

The logic of using bleach to get the level up right now instead of waiting for the SWG is pretty simple. If the pool was covered, there was no light, so no algae. Once you have light, any algae spores can start multiplying. An algae bloom can consume FC faster than the SWG can make it. Why not just kill it before it grows? Then the SWG just has to maintain the level.

This is assuming the water is clear. If the pool is green or cloudy, or even if there's just a few patches of algae, then you need to SLAM it.

Get the water circulating and then run some tests. Then decide what you need to add and in what order. If you're unclear, post test results here and someone will be along to advise you.
Aug 22, 2016
Charlotte NC area
Thank you all for the replies!

I am familiar with PoolMath and differences in target FC level based on CYA level, and what is appropriate for an AGP using SWG. (Thanks for a great forum, TFP!!)

My confusion was over Magnum32's post (the "sticky" one at the top of this forum!)...

Shock the pool with any chlorine shock product. This is available in liquid or granular form. You want to add enough to raise the chlorine level of the pool to at least 3.0 ppm.
I just needed to understand if there was a good reason to use a "shock" product versus just using bleach, CYA, and Acid or Baking Soda to adjust the levels as needed.

Jim and Richard have answered that for me. Thank You! :)

So to be clear, if my pool appears clear throughout, and I can bring my levels into a good balance within a few days, then I shouldn't need to "SLAM" it, right?

Thanks again!


TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
NW Ohio
Thank you for pointing that out, I just took a look and that post feels extremely dated. Probably comes from being 9 years old. Quite a bit of terminology has changed since then, and procedures, so I will bring that up to those in charge.

Once you bring things to level and the water is clear you should be fine, but keep an eye out for any unusual chlorine level drops and potentially run an OCLT if you notice any.


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
Aug 10, 2012
Thanks for pointing out the inconsistencies in this sticky. We have made appropriate corrections.