SLAM: First time SLAMing. Big FC overnight drop!

BattleOfYakima

TFP Guide
Apr 15, 2016
1,683
Central Florida
phappy:
2-3ppm is the "site average" so to speak. Some pools 1ppm/day others 4ppm/day. Lots and lots in the 2-3 range. Sun degrades some and some gets used to break down organics that blow in. Our dear friend bleach/chlorine/sodium hypochlorite is a real superhero sanitizer, but has its limits. It doesn't know the difference from a leaf, pollen, tree branch, algae, bacteria, or insect. It just goes to work oxidizing it if it is in the pool.

do you still put in the "typical" 2-3 ppm?
No. What's important is the FC is in the target range. It doesn't matter if you had to add .5 ppm or 5ppm. The FAS-DPD test allows us to add only what we need with little waste. That's one of the reasons many of us say it is an investment that pays for itself in bleach savings. By keeping your FC in or just above target for your CYA, you're keeping your FC well protected from sun degradation while maintaining a responsible buffer of available/active sanitizer to oxidize/kill contaminants that would love nothing more than to green your pool and get you sick.

Pools, like pets, cost money. They need to be fed or they get sick, or worse. As for how much money it costs to maintain your FC, now that's something we can work on! No matter what though, FC must be regularly replenished, either via SWG, bleach/chlorine, or one of the other methods. Each method has trade offs and limitations. Most people conclude that either SWG or bleach is best for them. Those who go bleach sometimes upgrade to an automatic bleach pump.

To answer your specific question though, a 26,730 gallon pool requiring 3ppm added, if using 10% would indeed be 103oz aka 3qt1cup, and yes, that's most of the jug. The whole jug adds 3.75 assuming it is fresh.

$3.50 a bottle might be a number we can get down though, depending on your local options. Depending on water temps, a SWG could be cheaper if bleach prices are high in your area.

Important note - daily FC demand is highest this time of year. My bleach cost per day in the summer is 5x what it is in the winter. Contributing factors include: bather load, water temp, rain, UV index, insect load, summer organic debris (grass clippings, pollen, flowers, etc.), and such.
 

phappy

Well-known member
Aug 25, 2013
45
Is it dead algae/debris....or is it undissolved Cal-Hypo shock ?

Yes, this is the question I'm at now. I decided to use Cal-Hypo 56% (HTH from Walmart) because the pool has low HC anyway. As soon as I used it, the FC went up to the SLAM/SHOCK level as intended. I sprinkled it around the deep end, and it some did fall on the bottom, so I brushed it up.

The next day (I'm continuously running the pump/filter), there are areas or trails of "gunky" substance on the bottom of the pool. My question is...Is this dead algae (proof that the CL is working), or is it undissolved Cal-Hypo shock still? I again brushed it up this morning....and seven hours later it has settled back down on the pool floor. It is a whitish/tan colored gunk substance.

So...I'm guessing since it settled once again after I brushed it that is IS indeed dead algae? And this should be vacuumed. But I wanted to ask before I do so, b/c if it is valuable shock that hasn't yet dissolved...then it's a waste to vacuum it (especially if I put in on Waste).

Also, I am not at the end of my FSD-DPD reagent! Of course, right? So I was hoping I could only take a 5 ml water sample, then divide the results by 4 instead of 2 when I use the 10 ml water level?

Thanks for your help guys.
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
Cal-Hypo will dissolve quickly and that is most likely dead algae.

If you use a 5ml sample, each drop equals 1ppm.

However, your margin of error will increase as well. Best to use a syringe or other accurate way to measure the 5ml.
 

Oly

Gold Supporter
Jun 28, 2017
1,559
Fresno, CA
Yes it sure sounds like dead algae and it will vacuum up but watch your pump pressure and be prepared to clean the filter soon. Keep a close eye on your overnight FC usage, you will know when the the tide is turning. When you get the suspended algae out of your water the clarity will be noticeably better especially at night with the pool light on.
 

phappy

Well-known member
Aug 25, 2013
45
This is getting tiresome. 15th day of SLAMMING the pool...

I realize the first week is basically a "throw away", as I am confident the Diamond Clear Mega Shock 12.5% liquid shock was highly degraded. So I was using bad chlorine.

Last night, I tested and the FC was low, so I put in enough CL (per Pool Math) to get it up to the FC 15ppm Shock level. (The SHOCK level changed from 14 to 15 b/c my CYA was actually a little low and I added some a few days ago) I did not test afterwards.

This morning 9AM: I tested early before the sun hits the pool and the FC was 14.5ppm! So I thought this was victory! The CC took one drop to clear out the pink, so 0.5ppm or less.

But I have continued to test during the day today:

12:30PM: FC 10.5ppm ! (added the Pool Math recommended amount)
4:pM: FC was 11.5 ! (again added the Pool Match recommended amount)

Why are these large FC drops happening?

Also, I do continue to find these trails & spots of light white/tan colored gunk substances. I vacuum them up in the filter (Some I've vacuumed to Waste, sometimes to Filter). They seem to emerge after I've put in bags of Cal-Hypo granular shock.

Could my Hayward S240 pool filter be somehow blowing back a substance in to the pool? How can this type of issue be diagnosed? And could this type of issue cause the issue of such large FC drops?

Thank you guys & gals as always for your help.
 

phappy

Well-known member
Aug 25, 2013
45
I may have had an "Eureka!" moment. Thanks greatly for your help & advice to this stage. I tested for the Overnight Free Chlorine Drop twice this morning. Last night the FC was 15.5ppm

- First test: FC 15.5 ppm !
- Second test (~20 min later): 14 ppm

So...would this signify that the SLAM process is actually over? Or do I keep it going for another day to make sure it's over? (I'd rather not, as tomorrow I have a big change in schedule & will be tough to test)

And if SLAM is over. What are my next steps? Just let the FC drift back down to the recommended FC 5 ppm daily level?

There was still some slight sediment/gunk in trails on the pool surface. Not as much as prior. I vacuumed it up. Do you think it is okay to put the Hayward Pool Vac in the pool now & start using it? I had been doing manual vacuuming.
 

BattleOfYakima

TFP Guide
Apr 15, 2016
1,683
Central Florida
I'm somewhat hesitant to allow an OCLT based on 5ml, but in this situation, given the combined evidence of the last week, I suggest this:
Do OCLT when you get more FAS-DPD, for now:
Let FC fall back to target, but not below please. Treat lower target like min until we're 100% sure.
Use auto cleaner as you wish
No rush, but if you can, capture some junk in turkey baster, zip lock, cup, pot and bring to surfacre, pour on piece of paper/towel and photo for us, describe texture/feeling

You've done great, we just want to make sure you're really setup for TFP cruise control
 

phappy

Well-known member
Aug 25, 2013
45
Thanks BattleOfYakima! I so much appreciate your help & guidance through this process.

I forgot to mention that the good OCLT tests were indeed done at the normal 10ml of water! The new chemicals arrived yesterday and I was able to go back to 10ml water.

Since you mentioned hesitancy at 5ml, does it change your idea of how to proceed knowing that the tests were indeed done with 10ml water (as normally done)?
 

phappy

Well-known member
Aug 25, 2013
45
Darn...I just tested again (3PM EST, six hours after my morning test)

The FC has dropped to 11.5 ppm! Why?
And now the CC is a full 1.00 ! This morning it was essentially "0.00"!

Any ideas as to what may be happening? Today there is not much direct & strong rays from the sun either.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,976
Franklin, NC
Darn...I just tested again (3PM EST, six hours after my morning test)

The FC has dropped to 11.5 ppm! Why?
And now the CC is a full 1.00 ! This morning it was essentially "0.00"!

Any ideas as to what may be happening? Today there is not much direct & strong rays from the sun either.
3 - 4 ppm loss of FC during the day is to be expected.

What was the bather load during the day?

The bather load may also factor in to the CC. Lots of kids?

CC is burned up by UV rays of the sun.
 

phappy

Well-known member
Aug 25, 2013
45
Thank you for your reply & help, tim5055. I didn't know that a 3-4pm loss in FC is an expected loss. There was no one using the pool today at all. I thought perhaps a drop of 1-2 ppm (preferably 1 pmm) during a day would be normal. Our pool does not get daily activity/swimming at all.

Now, with the Combined Chlorine. Why would that jump form almost zero to 1ppm? You said it is burned up by the UV rays of the sun. But if your CC is above 0.5ppm, doesn't that mean you have to SLAM? I thought b/c there was a OCLT of essentially zero, and a CC test of essentially zero this morning that my SLAMming was over?
 

BattleOfYakima

TFP Guide
Apr 15, 2016
1,683
Central Florida
You will see your largest daily FC losses during the highest temperatures and most intense sun - or in other words, about now.
Via ABCs of Pool Water Chemistry:
Combined chlorine is an intermediate breakdown product created in the process of sanitizing the pool. CC causes the "chlorine" smell many people associate with chlorine pools. If CC is above 0.5ppm, you should SLAM your pool. CC indicates that there is something in the water that the FC is in the process of breaking down. In an outdoor pool, CC will normally stay at or near zero as long as you maintain an appropriate FC level and the pool gets some direct sunlight.
Expect to see some CC from time to time, but then later on expect it to be gone. The idea with monitoring them is to use it as an indicator if there is a problem, both by single reading high values like 1.5+ or continuously having 1.0+ all the time. At least that's my current understanding...I'm always learning :)

Your pool seems to be good to go. Keeping track of your total daily FC losses for a few days when you can and doing an OCLT one day later this week will give you a really clear snapshot of your pool's health. This time of year, at your CYA as long as you're not losing more than 6ppm /day and passing OCLT - you're good and the discussion becomes whether to raise CYA or not to minimize daily loss, or tough it out. Pros and cons each way.