Vacation plan: thoughts on super-shocking?

[Soximus]

Hi all,

I’m sure this has been discussed before, but after diligently searching the forums (I read through several old threads), I couldn’t find a clear answer! Sorry if I missed it somehow.

My daily FC loss is 2-3ppm (it’s rarely 1ppm, on low use/low sun days, and it’s rarely 4ppm on high use/high sun days). We’re going away for a week. Is there a reason I should NOT take my SLAM level, then add an additional 17.5ppm’s worth of bleach (7 days x average daily loss of 2.5ppm = 17.5ppm loss per week), and then add enough bleach to get it to that level right before we leave? So if my target FC for a SLAM is 18, I’d add enough bleach right before leaving to get the pool to 35.5ppm FC. Then when we got home I’d expect the FC to be right around SLAM level. We don’t expect anyone to use the pool when we’re away.

I suspect there’s something I don’t understand about FC loss (maybe it’s not linear), but… I’m excited to learn!

Thanks

 

[Katodude]

You risk bleaching your liner if you go above SLAM level.

If your CYA is not too high, I would get a floater with a bunch of pucks.

 

[DorsalSpine]

Either get a floater with pucks or run your FC up to slam level and just let it drop. If your SLAM level is 18 and you loose 2 per day you will be down to FC=4 after seven days. That's low but not automatic green swamp low. I'd go with a floater or a neighbor that can add some LC for you mid week. Make it easy for them. I usually leave a full bottle or a partial bottle (depending on how long I will be gone) and just tell them to add it all on a certain day.

 

[Newdude]

Hey Sox. We recommend going to SLAM levels all the time. Over SLAM risks both liner issues as said above and possibly even equipment damage.

On top of that there is more at play as well. The FC burns off as a % in relation to the CYA. I don’t have the #s in front of me, but let’s use 30% as an example for your CYA. If your FC was 3 today you would lose roughly 1 FC if today was an average day. If the FC was 9 today, you’d lose 3. It’s not that big of a deal under 10. But if you went to 35.5 like you thought, you’d lose 10.6 FC and be at 24.9 FC on day 2 and 17.4 on day 3. Again, this example is ignoring other factors like exactly how strong the UV demand is from the sun each day while you are away, but you get the picture.

 

[Soximus]

Hey Sox. We recommend going to SLAM levels all the time. Over SLAM risks both liner issues as said above and possibly even equipment damage.

Wait… SLAM levels all the time?? That’s a new one for me. Pool Math app has “recommended” and “target” numbers, and then a SLAM toggle (which is, obviously, much higher than either “recommended” or “target”). What would be the point of the R or T numbers if we’re supposed to be at SLAM levels of FC all the time?

On top of that there is more at play as well. The FC burns off as a % in relation to the CYA.

Ah ha! That makes sense, intuitively. I suspected FC loss wasn’t linear… thanks for this info and for the helpful example!

 

[Newdude]

Wait… SLAM levels all the time?? That’s a new one for me. Pool Math app has “recommended” and “target” numbers, and then a SLAM toggle (which is, obviously, much higher than either “recommended” or “target”). What would be the point of the R or T numbers if we’re supposed to be at SLAM levels of FC all the time?

No no no no.

Simple miscommunication here. We recommend that folks bring their pools to SLAM for a duration *all the time*. Like for the duration that they are away on vacation. Totally safe to start vacation at SLAM and go back to regular operating levels when they come back.

Things don’t always come across as clearly as they’re meant. Good show old chap. Carry on.

 

[Soximus]

No no no no.

Simple miscommunication here.

Hahaha… phew! Thanks for clarifying. For a minute there I thought I had REALLY missed the TFP boat…


I can do some googling, but: Earlier you mentioned using a 30% multiplier when doing a FC-loss calculation as related to CYA; I’m wondering if it’s possible to dial that number in a bit more, maybe. If you happen to have it handy… is there a table/calculator that would perhaps indicate what the expected FC loss would be (assuming zero use), for pool volume X, CYA level Y, UV light level Z, starting FC level Q? Or something like that?

 

[Newdude]

is there a table/calculator that would perhaps indicate what the expected FC loss would be (assuming zero use),

The is always science out there to be found. But in this case it’s far beyond my *basic* understanding of it.

2 folks who blow my mind with science and/or math on the reg are @JoyfulNoise and @JamesW. I will punt this to them.

 

[Newdude]

*but only for the knowledge, because you raised a great question, not because it’s a good idea to fine tune how high above SLAM you would in theory need to go. That is not a good idea. At. All. But science is fun so let’s learn away.

 

[Bvacchiano]

Now you see why so many on here recommend an SWG. You can keep it generating chlorine however much you want from the click of your phone..
I personally add LC to get to SLAM level or at least close before going on vacation then turn up the SWG a little. Ie my daily FC loss is around 3. Fix SWG to make 4 a day.

 

[JoyfulNoise]

No, there is not something that simple. FC loss is not constant with concentration but increases with FC when CYA is held constant. The loss rate at 4ppm FC is lower than 20ppm FC. So even raising the pool up to SLAM level will cause the FC loss rate to be initially higher then taper off.

You should simply raise you FC a bit (and lower pH if you need to) and then add a puck floater to the pool that will add chlorine slowly. You may dip below your minimum but I doubt your pool will go full blown swamp green while you are gone. Even if algae does start, a quick SLAM will fix it.

Any teenage neighbor kids willing to make a quick $40-$50 to come over each day and add a premeasured soda bottle of bleach to the pool? I did that once as a kid for my neighbor and he just called my mom out of the blue to ask her. Easiest $20 I ever made … I think I spent it all down at the 7-11 on candy and video games. Space Ace was a big deal when I was a kid.

 

[Soximus]

*but only for the knowledge, because you raised a great question, not because it’s a good idea to fine tune how high above SLAM you would in theory need to go. That is not a good idea. At. All. But science is fun so let’s learn away.

Totally agree, on all counts!