rationale for clear water criterion for end of SLAM?

[singingpond]

I've searched and read, but haven't found a specific answer...

One of the criteria for successful end of SLAM is crystal clear water. Is this just an empirical observation (i.e. do it because it works), or is there some reasoning/understanding behind it? In other words, if all the algae is dead (presumably evidenced by passing OCLT and having minimal CC), why is it necessary to maintain shock levels while waiting on filtration?

Does the dead algae provide nutrition for new algae or for other life forms, thus encouraging a new outbreak in the water? Is the thought perhaps that cloudy water keeps the pool owner from accurately scrubbing off all remaining (live) algae spots on the liner? Is there some other reason?

Those of us with crappy filtration systems (seasonal pool owners using out-of-the-box equipment for pumping/filtration) would like to know.

Also, a related question... SLAM protocol calls for keeping pump on 24/7. However, the only way I can get our pool clear after killing algae (working with a woefully inadequate filter, for the moment anyway) is to turn the pump off, wait for the assorted fine junk to settle (requires hours without circulation), and then vacuum to waste (which is accomplished by siphoning the stuff at the bottom overboard). Is that period without circulation a major problem?

 

[JohnT]

I'm somewhat of a contrarian on this as well. I don't maintain shock level once the pool quits eating chlorine overnight. It can take a week or more for my pool to clear after algae. A lot of new-to-TFP pool owners still have the idea that shock is a one time thing and they quit too early, so it's better that the SLAM too long rather than not long enough.

The reason for running the pump when SLAMing is to keep the chlorine mixed in with the algae. With no circulation, you could get areas within the pool of low FC that could hamper the fight. I'd say get through the major chlorine consumption stage before you shut the pump off to settle the debris and you will probably be good. Just make sure recent chlorine additions have plenty of time to circulate before you shut it off.

 

[Nuvene]

I think part of it is that the higher chlorine will actually breakdown the dead algae therefore helping with the clearing process as well as some getting filtered out.

 

[chem geek]

If there's minimal overnight chlorine loss then the chlorine likely isn't going to do much more to the algae and at that point it's a filtration issue. The criteria are more about making sure that growing algae is killed even if it doesn't show up as a lot of chlorine demand. For sure one wants the chlorine to bleach out the chlorophyll so that the algae is killed. Chlorine also oxidizes or makes chemicals more polar so they may coagulate together more (analogous to microflocculation from ozone).

So yes, if you've shocked and the green is gone and there's minimal chlorine demand and the water is just cloudy and needs to get cleared, then the chlorine level can probably be lowered to normal levels while the filtration clears the pool.

 

[singingpond]

Thank you all for the thoughtful responses!

 

[adrob2]

Great thread, I had wondered the same thing but hadn't asked!