SLAM necessary without corresponding drop in FC?

[C3Cl3N3O3]

I like to have the pool opened by Memorial Day, but made a few mistakes this year. Here are my numbers:

FC: 3 - 6
CYA: 30
TA: 80
pH: 8.1

At no point did the FC drop below 3. However, after the rain last week I ended up with a lot of particulates in the pool. I presume some is pollen washed off the overhead trees which were really dry. Instead of vacuuming, I've been running the quick clean mode on the pump and brushing a lot. But after a few hours a fine coat of dirt would reappear across the entire liner. I'm on day 3 of that. I've had mustard algae before and it's not that, just a fine brown particulate that brushes off easily.

So the pH had risen to 8.1, that was mistake one. It's down to 7.5 now. I'm running a VSP for the first time this year and getting used to it. I was slow to recognize that the sand filter needed a backwash, and my flow rates dropped off. I've taken care of that and deep cleaned the filter for good measure today. The sand is five years old.

I vacuumed the pool as well today, but the pool has deteriorated into a blue-green cloudy haze.

I'll go ahead and start the SLAM tonight. But would you expect an algae bloom to take hold without the FC ever dropping off? I'm not seeing an increase in chlorine demand, it has been around 2.5-3 ppm / day. Are there some dots that I'm not connecting properly here based on these clues?

 

[mas985]

When in doubt, an OCLT can sometimes confirm and algae problem.

 

[C3Cl3N3O3]

When in doubt, an OCLT can sometimes confirm and algae problem.

I may as well spend the chlorine now and get this thing moving in a better direction. It doesn't appear that it is just going to clear up on its own. But I will be sure to measure FC outside of daylight hours.

Is it possible to go an entire season without SLAMing? I'm really off to a bad start this year, but have issues like this every year. I'd like to understand why. My CYA/FC ratio is perfect. My pH drifted up, but I'm not sure that's the root cause of this. It did seem to coincide with the rain storm. My pool has always been unforgiving. You slip up in the slightest way and you PAY. Even if you don't slip up, you still might pay.

My pump schedule is 4 hours at 2300 RPM and 18 hours at 2000 RPM.

 

[mas985]

I rarely if ever "SLAM" my pool. I can usually see if things are headed in the wrong direction and just elevate FC a little (but below SLAM levels) for a few days and it is fine after that. The key is catching it early even if you aren't entirely sure that it is an issue. I think that the biggest issue most people run into is that they wait too long before taking action and then things get out of control after which a SLAM is the only way to fix it. The rate at which algae is eliminated is related to the amount of algae in the water and the level of FC/CYA. So the more algae in the water, the higher the FC/CYA ratio needs to be although the SLAM levels seem to be enough even for the worst cases which is why it is often suggested. It is fool proof but not always necessary to combat algae.

 

[C3Cl3N3O3]

Yeah I would agree with that. But the fact that I didn't see any spike in chlorine demand camouflaged the issue for me.

I'm running a lower CYA this year (30) than last (40). I get a lot of direct sun, and maybe this isn't going to work out. I do use trichlor for a few weeks here and there when travelling and like to keep some runway for it to rise a bit. I may have to punt on that and go to 40 or 50 if this is how it is going to be all summer.

 

[mas985]

With a lower CYA, it is important to measure FC at the end of day to directly see the effect of UV extinction on the FC level.

 

[C3Cl3N3O3]

Well my inaugural SLAM of 2021 is underway.

My FC was around 7 ppm and I added 2 pounds of 65% cal hypo. I waited 30 minutes and tested. That should have increased by 8 ppm, but instead it increased by 12 ppm. A 50% overshoot, I wonder how that happened? These are In The Skim 1 lb packs. I weighed them and they are in fact one pound each. What the heck?

So should I run the VSP at the usual filter speed (2000 RPM) or the skim speed (2300)? Does it really matter?

 

[mas985]

It doesn't matter that much as long as the pump is running and circulating the water.

 

[C3Cl3N3O3]

Good enough.

So I was in disbelief regarding that 19.5 FC reading. I waited another hour and tested again, thinking maybe the VSP needs more time to mix. It was dusk before, now it is pitch black and I got 18.5 FC. That is sort of baffling.

 

[wireform]

C3,
Can I ask why aren't you slamming with liquid chlorine? The PH should have been 7.2 but not much you can do now other than if you are darn sure of the pool capacity with poolmath see how much MA it would need to get it from 7.5 to 7.2 and get that in there too. Overshoot is waste and not great for the liner.

 

[C3Cl3N3O3]

C3,
Can I ask why aren't you slamming with liquid chlorine? The PH should have been 7.2 but not much you can do now other than if you are darn sure of the pool capacity with poolmath see how much MA it would need to get it from 7.5 to 7.2 and get that in there too. Overshoot is waste and not great for the liner.

I wouldn't expect LC would be more precise. Unless you are into decoding Julian dates, LC is mostly pot luck. I do have a supply.

The SLAM process says I can do a pH up to 7.5 so that's what I did.

SLAM - Shock Level and Maintain

We’ve all had to deal with a green pool. Clear algae from your pool with a SLAM! Read here to use shock level and maintain to clear your pool.

www.troublefreepool.com

 

[C3Cl3N3O3]

OK I checked the FC fifteen minutes before sunrise and had lost around 3 ppm overnight.

In reassessing the situation with fresh eyes today I've deemed this to in fact be mustard algae again.

After brushing the clarity has improved modestly from yesterday. Yesterday was a complete blue-green mess after brushing. There is less accumulation on the walls today. The filter pressure hasn't increased.

So has running a lower CYA this year put me at higher risk of this? I've had it twice before but it really came on fast and strong this year despite being a well-maintained pool. Maybe kick it back up to 35 or 40? One issue with 30 is that it is at the limit of the range (30 - 50) and also right at the limit of 2 ppm on the pool calculator. At 31 it goes up to 3 ppm. So I feel I might be too close to the edge.

 

[mas985]

These are the targets you should be using:

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

I would not go below 10% of CYA if you manually dose the pool.

When do you test and dose? Do you still use the Rainbow?

 

[C3Cl3N3O3]

These are the targets you should be using:

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

I would not go below 10% of CYA if you manually dose the pool.

When do you test and dose? Do you still use the Rainbow?

OK that has the target range at 4-6, I may have gotten down to 3 but no lower. It doesn't matter, I dose to the approximated max (6) with LC, but FC can drift downwards between testing of course. I test in the afternoon, once a week when things are running smoothly. I can move it back a few hours to sunset. Maybe test twice a week? I'm testing every day as I work through the Mustardocalypse.

The Rainbow is for when I'm travelling. I have to say it does a really good job at that. People who think chlorine floaters are "just as good" in that scenario must take really short vacations (or have really good neighbors).

 

[mas985]

When fighting algae, it is important to test nearly every day since you really don't know how fast the algae is consuming the chlorine.

 

[C3Cl3N3O3]

Well things are moving slowly in a good direction. Last night I didn't see any FC drop. The clarity has improved to a 7/10 or so today. There was still some brownish yellow debris brushing off this afternoon but it is less each time. That mustard is tenacious stuff but tonight may be the last of the SLAM. I don't believe it will take the full week for the filter to clear it.

 

[Newdude]

OK that has the target range at 4-6, I may have gotten down to 3 but no lower. It doesn't matter, I dose to the approximated max (6) with LC,

No no no no no no no no no no nononononono
6 is not max. SLAM is the Max. 6 is barely acceptable if you lose 3PPM daily. As the summer ramps up and the UV increases you’ll lose even more.

Target range is basically the bare minimum that needs to be done. You can decide that it’s dancing the fine line too closely and choose to run a little higher so when you lose FC you drift back into target range and are still golden. Many of us treat target as our minimum. *actual* minimum is a cliff that you never ever want to look over. Or even stand close to.

I always say to stay far away from that cliff so you can call 911 when some Millennial goes over trying to take a selfie.

 

[C3Cl3N3O3]

So is

No no no no no no no no no no nononononono
6 is not max. SLAM is the Max. 6 is barely acceptable if you lose 3PPM daily. As the summer ramps up and the UV increases you’ll lose even more.

Target range is basically the bare minimum that needs to be done. You can decide that it’s dancing the fine line too closely and choose to run a little higher so when you lose FC you drift back into target range and are still golden. Many of us treat target as our minimum. *actual* minimum is a cliff that you never ever want to look over. Or even stand close to.

I always say to stay far away from that cliff so you can call 911 when some Millennial goes over trying to take a selfie.

Thanks, I'll start dosing to where I believe 8 or 9 is moving forward. I have definitely slipped below 4 by a hair.

 

[CrystalRiver]

With a history of mustard algae, you should be running your FC "hot" for an extended period to make sure it doesn't come back. I would aim to maintain it above 6 at all times at CYA 30. You can safely go up to 12.

As for the unexpectedly high FC following your dosing, there's two reasonable causes. One is testing error on your initial test, so your starting FC was higher than you think. The other is that your pool is much smaller than you think.

Your SLAM is not done until you have crystal clear water, no cloudiness or debris on the bottom or patches on the wall. Then you need to follow the mustard algae instructions.

 

[C3Cl3N3O3]

With a history of mustard algae, you should be running your FC "hot" for an extended period to make sure it doesn't come back. I would aim to maintain it above 6 at all times at CYA 30. You can safely go up to 12.

As for the unexpectedly high FC following your dosing, there's two reasonable causes. One is testing error on your initial test, so your starting FC was higher than you think. The other is that your pool is much smaller than you think.

Your SLAM is not done until you have crystal clear water, no cloudiness or debris on the bottom or patches on the wall. Then you need to follow the mustard algae instructions.

I checked my Fas-Dpd reagent, it has a best by date of 2019. I bought it in 2019. When these reagents get old, do they over-report FC like that? If so, that pisses me off.