Ben's Best Guess vs. Chem Geeks Best Guest

[crazycanuck]

OK, I know there are two best guess charts... which one are most people following? I don't mean for people to picks sides or favourites, its not about popularity, I just want to know which chart is more... ummmm. accurate.

I see chem's chart seems to have a higher percentage of FC vs. CYA. 60% I think vs. Ben's 50%. for shocking.

 

[Rangeball]

Where is Richard's chart?

I thought he recommended min FC as 7.5% of CYA, target FC ast 11.5% of CYA but I don't recall seeing a chart or even what he says about shocking.

Got a link?

 

[JasonLion]

At low CYA levels Ben's chart is probably better. Chem geek did not take into account needing to maintain some minimum residual or the inaccuracy of CYA testing (as best as I can tell). Ben's chart does take both of those into account.

In the mid-range, where we normally recommend pools be, they essentially agree with each other.

At very high levels of CYA I believe that Chem Geek's chart is better, but there isn't much experience with very high CYA levels to compare to and some of us have been wondering if Ben knew something we don't or if it was simply a rare situation and Ben didn't have much experience in that range.

(Chem Geek's chart is in The Stickes section of this site, Ben's chart can be found by following the link in my signature.)

 

[Rangeball]

(Chem Geek's chart is in The Stickes section of this site)

Jason, where? I've been to every forum and subforum, and unless I'm missing it it's not there. Also when I hit the "The Stickies" link at the top of the page under the TFP header, it lists it, but no link to get to it.

What am I missing?

 

[JohnT]

(Chem Geek's chart is in The Stickes section of this site)

Jason, where? I've been to every forum and subforum, and unless I'm missing it it's not there. Also when I hit the "The Stickies" link at the top of the page under the TFP header, it lists it, but no link to get to it.

What am I missing?

Go to "The Stickies" and select the triangular icon on the left side of the page next to the topic you wish to read.

 

[Rangeball]

Thanks Jon.

I swear I scrolled over everything on that page, and couldn't click anything.

So, what's one to do above 120 ppm of CYA?

 

[MikeInTN]

Thanks Jon.

I swear I scrolled over everything on that page, and couldn't click anything.

So, what's one to do above 120 ppm of CYA?

Start draining and refilling.

 

[crazycanuck]

At low CYA levels Ben's chart is probably better. Chem geek did not take into account needing to maintain some minimum residual or the inaccuracy of CYA testing (as best as I can tell). Ben's chart does take both of those into account.

In the mid-range, where we normally recommend pools be, they essentially agree with each other.

At very high levels of CYA I believe that Chem Geek's chart is better, but there isn't much experience with very high CYA levels to compare to and some of us have been wondering if Ben knew something we don't or if it was simply a rare situation and Ben didn't have much experience in that range.

(Chem Geek's chart is in The Stickes section of this site, Ben's chart can be found by following the link in my signature.)

Thanks for the insight... it was really more about the shock levels... it varies by about 2.5 to 5ppm in some cases.
There almost needs to be a best guess chart for SWG's too.

 

[SeanB]

I think Chem Geeks chart probably has more research behind it - it may not actually be fair to call it a "guess."

 

[Rangeball]

Thanks Jon.

I swear I scrolled over everything on that page, and couldn't click anything.

So, what's one to do above 120 ppm of CYA?

Start draining and refilling.

If it was my pool, in a heart beat

It was my first recommendation.

However, it's my dad's, and he doesn't want to as he plans on getting a new pool next season

 

[chem geek]

Jason is correct. When I sent the data to Sean to post I wrote up caveats, but they didn't make it to the Sticky. The chart shows constant disinfecting chlorine levels of 0.03 ppm for the Min FC, 0.05 ppm for the Target FC, 0.07 ppm for the Yel/Mstrd FC (which is similar to Ben's Max column), 0.3 ppm for the Shock FC, and 0.7 ppm for the Yel/Mstrd Shock.

Obviously, you need a certain minimum FC level regardless of the CYA level so at very low CYA levels (probably below 30 ppm CYA) the chart no longer makes sense. As for what that minimum FC level should be, it depends on your pool's chlorine usage and how often you add more chlorine. You want to have enough FC to be there in reserve for a localized "accident" or local algae growth or organic debris (e.g. pollen). Obviously, I can't quantify this, but for an outdoor pool it's probably somewhere in the neighborhood of 2 or 3 ppm FC.

The rough rules I give of 7.5% of the CYA level for Min FC, 11.5% of the CYA level for Target FC, 15% of the CYA level for Yel/Mstrd FC, 40% of the CYA level for Shock FC, and 60% of the CYA level for Yel/Mstrd Shock are very reasonable approximations. You can see that from the chart -- they only fall apart at very low CYA levels near zero.

The chart or approximations work rather well tracking Ben's Min and Max columns, but it doesn't track his Shock column very well. This is because my chart is based on disinfecting chlorine level so will determine the RATE at which chlorine will kill algae so the values in my chart will all kill algae at the same rate. There are two issues, however. At low CYA levels, the lower shock FC levels may "run out". So again there needs to be some minimum FC level for shocking for any CYA level. This depends on the amount of algae there is and how often you add chlorine. I would guess that a minimum of 10 ppm is about right. The other issue is at higher CYA levels. Though I am confident of the chemistry behind using about 40 ppm FC at 100 ppm CYA to shock a pool (for green algae), those with vinyl liners may wince. Also, the CYA test isn't prefectly accurate and when at such high chlorine-to-CYA percentages, errors in CYA have the disinfecting chlorine level swing quite a bit. So using a lower FC of perhaps a minimum of 25% of the CYA level would still kill algae in a reasonable time period, but would do so more slowly than at 40%. Technically, any FC level above the "Min" column will kill green algae faster than it reproduces, but in an algae bloom local FC levels drop a lot so too little FC isn't good.

Finally, the SWG level is a tough one to set since not everyone has success at lower levels though most do. If I were to hazard a guess based on the rough 3 ppm FC at 60-80 ppm CYA that most pools seem to be able to handle to keep away green algae, then I would say that for SWG pools the disinfecting chlorine level for the "Min" which is also a "Target" due to near-continuous chlorine introduction is around 0.02 ppm which translates to an FC level of around 4.3% of the CYA level. We could add another column to the chart where I more accurately calculate the FC numbers, but most people run 60-80 ppm CYA so just saying 3 ppm FC minimum works for most SWG pools (maybe 3.5 ppm FC is better for the 80 ppm CYA pools).

Richard

 

[Rangeball]

The rough rules I give of 7.5% of the CYA level for Min FC, 11.5% of the CYA level for Target FC, 15% of the CYA level for Yel/Mstrd FC, 40% of the CYA level for Shock FC, and 60% of the CYA level for Yel/Mstrd Shock are very reasonable approximations. You can see that from the chart -- they only fall apart at very low CYA levels near zero.

Richard

at 160 ppm CYA that's 64 ppm FC, or for my Dad's pool 19 .75 jugs of 6%.



And I thought maintaining at 18 ppm FC was bad... He had a terrible algae bloom when the pool maintenance guy ignored him after opening. Finally they did a drain and refill, but they of course added stabilizer and shocked it with dichlor a few times and ignored it again, and it started turning green. That's when I got involved, and I had them hit it with 7 jugs of 6% immediately, 4 more later then 3 more the next morning. Pool waters been clear since, but based on the 40% figure for shock above at his CYA of 160 we've never shocked it.

Right now I have it at 18 ppm FC, with no CC. I guess since no CC, no need to shock. It was as low as 8 ppm FC with no CC. I'm wondering if they'd be better off in the long run at 8 ppm...

 

[crazycanuck]

LIke Richard said, when your CYA gets to 160 level, I think the best guess charts have a larger level of inaccuracies, especially since most people who have it that high usually drain and refill till its in a managable level.

 

[chem geek]

Rangeball,

The point is that at 160 ppm CYA if you had used 40% or 64 ppm FC then it would have cleared up as quickly as pools with lower CYA and lower FC shock levels (at least, that's the theory). But any amount of chlorine higher than 7.5% or 12 ppm FC would have killed the algae, though just barely faster than it reproduces. 7 96-ounce jugs of 6% chlorine in 15,000 gallons would give 21.6 ppm FC plus the additional 7 you added later so though much of the chlorine probably got used up quickly, you may have added up to 40 ppm FC (unless the pool was larger than I guessed). That's still a very healthy amount of chlorine. That's why I said that even 20-25% of the CYA level would give a reasonable algae kill rate and that would be 32-40 ppm FC which might have been in the range you had.

Maybe the entire shock scale is actually too high. I just used the mid-point of Ben's CYA chart figuring that was a reasonably fast enough clearing of algae, but maybe that's overkill. I was just trying to get some consistency to it. So for shocking, the levels of chlorine just have to be quite a bit higher than the Min level and kept there consistently. How high you go is up to you and how quickly you want the algae killed (and how frequently you are testing and adding chlorine).

Then again, maybe there is SOME algae inhibition (though obviously not much given how well Ben's chart works to keep away algae) from the chlorinated isocyanurates (chorine combined with CYA). That, of course, would please the manufacturers of Trichlor and Dichlor to no end.

Richard

 

[Rangeball]

Thanks Richard.

As long as they keep on top of it, which they have for the past few weeks, hopefully they won't have anymore algae to contend with this season.

Next spring when they get a new pool, we'll do it right from the beginning

As for your last paragraph, well, wouldn't that be something

Hey, can you imagine any experiments I could do to test this, since I've got 13,500 gallons of water to experiment with? Something like set a clear open container of the water out exposed to the same conditions as the pool, and see what happens?

They won't be back for 8 days or so...

 

[chem geek]

Well, though it is rather easy to test for the minimal inhibition level of chlorine and how that relates to FC and CYA, it is much harder to see what shock levels would do since it's a rate thing so you have to see how quickly algae goes away. The hard part is starting with the same amount of algae under different conditions and then seeing how quickly it breaks down under different CYA/FC levels. The fact that the Ben's chart and my chart work so well for keeping pool's algae free and that some users have experimented with using just a little more or a little less chlorine and see algae just go away or just come back (for mustard/yellow algae in particular) says that we've found the right levels and they DO track the disinfecting chlorine concentration -- NOT the FC level.

The main remaining issue with chlorine is what happens with high phosphates. There is one pool owner at this thread on another pool forum who seems to have phosphates and algae that will not stay away at normal FC levels given the CYA (that 3 pool stores has said is around 60 ppm). However, he doesn't have a good test kit yet and may not have gotten rid of the algae completely yet either and I'm not sure how he's consistently measuring the higher chlorine levels without a good test kit. After he gets his test kit, then we'll know more. So the "experiment" is with a bucket of water with "ideal" and very generous phosphates and nitrates (i.e. fertilizer) and seeing if our CYA/FC charts still hold in that nutrient-rich environment.

Richard

 

[Rangeball]

Thanks. I'm just at a loss to recommend what they do. Maintain at 18 ppm FC? They were clear with 8 ppm. Flip a coin, I guess.

I did add the initial dose of poly they had. I'll test their FC again tonight, as it was holding at 18 ppm (I've been adding 1.65 ppm nightly) but I understand I probably lost some of this due to the poly. If so, I'll take it back up to 18 and monitor it for a few nights.

I just don't want them to ever get near an algae bloom again, with a 160 CYA...

 

[chem geek]

Since the "target" number has a lot of safety margin in it and it's really the "Min" where the FC should never drop below, the 7.5% of 160 or 12 ppm is more of the minimum for your Dad's pool. As for 8 ppm, which is 5%, it is possible that your Dad's pool has other limiting factors of algae growth including lower nitrates or phosphates so that may be why 8 ppm FC seems OK. Again, remember that Ben's chart was developed with those doing manual dosing and you know how the FC goes up and down during the day based on usage and addition so there's probably some slack in Ben's chart even at the "Min" column (so the same would be true for my Min column since it was based roughly on Ben's chart as a starting point). But it does seem to me that pools that are more nutrient rich in nitrates and phosphates do need to stick to the chart numbers more while other pools can get away with lower levels. This is why I'd like to experiment with algae "ideal growth" conditions as a worst-case scenario just so we have something of a "guarantee".

One other thing to keep in mind is that algae doesn't look green to start with so if you are on the edge of killing algae fast enough, the pool water might just look "dull" or very slightly cloudy, not green.

Anyway, using PolyQuat 60 will be good insurance in your Dad's pool until the time comes for a partial drain/refill to get the CYA lowered.

Richard

 

[Rangeball]

Thanks. His water is crystal clear. But he does have that pollen/dirt/whatever it is accumulation that's been going around. Lot's of big trees relatively close to his pool.