How does my Nature 2 fit in this puzzle?

Hi - I'm new here :) I've been reading for a few days and I've just tested my CYA level so that I can use the best guess chlorine chart. My question is:
How does my Nature 2 fit in with the chart suggestions? My CYA is between 80 and 90 ppm (depending on the light available, it was hard to tell when to stop putting drops in the test tube). So, from the chart my min FC is 5 and my max is 10 ppm. But the claim on the Nature 2 is that you can lower the amount of chlorine needed by half. Is that true?

Right now my water is sparkling clear. I've been working hard to get the water balanced. I pulled the chlorine tabs from the pool a few days ago and I'm going to chlorinate with bleach, as suggested on this forum.

Here's my basic pool info:
I have an IG, 18,000 gal fiberglass pool (4' shallow end, 6' deep end). The water is currently 77 degrees, but it gets WARM in the summer - I've seen it at 94 degrees. I currently have a 12 year old 36 SF DE filter, but I have the replacement 48 SF one sitting the garage waiting to be installed this weekend. The pump is a Pentair Ultra-Flow 1.0 hp. I run a 3/4 hp booster pump to power the newly replaced Letro Legend sweep (the sweep has been doing a great job!).

My water chemistry is:
pH 7.3
TA 100 ppm
FC between 2 and 4 ppm
CYA 80-90 ppm

The fill water is:
pH 7.0
TA 110 ppm

So, I'm trying to figure out what FC level I should have in conjunction with the Nature 2. From there it would be helpful to know how much bleach to put in, and how often, to maintain that.

Also, would it be helpful to drain some of the water to try to get my CYA number lower? I've read some about the "best guess" reasoning, but it still freaks me out to see the FC level that high! I suppose that is just because it is beat into us to use between 1 and 3 ppm - the "safe" value.

Did I miss anything? Thanks in advance for your help!

PS - To the admin - I hope that your father is on the road to recovery - I've been praying for him and your family.

I can't really advise you regarding Nature2 or it's claims without exposing my personal bias about such products. That said, here goes:
Do they tell you exactly what's in it? If not, why? I've flippantly advised people to turn it off, cut it out, or pull out the cartridges. It may have a place but my guess is that it puts copper in the pool and I would not advise adding copper to a pool for a number of reasons. The first is aesthetic, copper stains pools, fingernails and light and colored hair green. Second (and more important) is sanitization copper is a pretty effective algaecide (really algae preventative) but a pretty poor sanitizer. Copper is dangerous because it can (with low FC advice) lead to a pool that looks clear(no algae) but can't kill the bacteria that gets washed away from the far end of a swimmers GI tract before it gets to the near end.

Quote:

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Originally Posted by Penuche

I've read some about the "best guess" reasoning, but it still freaks me out to see the FC level that high! I suppose that is just because it is beat into us to use between 1 and 3 ppm - the "safe" value.

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This is a common problem, but it is a psychological issue, not a pool issue. Unfortunately, this, and similar issues, are inflamed by chemically illiterate journalists and environmentalists, who think editorial deadlines or environmental passion can legitimately overrule simple facts.

However, as such, you have to decide what you're going to do -- suck it up, and go with the facts, or suffer pool problems because of unresolved phobias?

It might help to know that, until recently, the US EPA had NO upper limit on chlorine in drinking water. As a result it periodically happened that pool owners filled their pools with water that was "too high" in chlorine to swim in! Even today, the upper limit on chlorine in drinking water is 4 ppm (not 3!), and is a warning limit, meaning that the utility should make a reasonable effort to get it back down within a reasonable time. There is NO requirement to notify water company customers that they were briefly consuming water at 5, 7 or 10 ppm chlorine!

Several years ago, an unfortunate lady who shared your phobia, accidentally drank a few ounces of household bleach she'd left sitting in a juice glass. (Why? No idea!) Panicking, she called 911, and was told to drink some water to dilute the bleach. She drain 2 gallons and died!

She died from the same problem that put my dad (who's doing much better, thank you) in the hospital -- electrolyte imbalance. In Dad's case, he had not been drinking enough; in her case, it was WAY too much! It's my understanding, that if she'd done NOTHING, should would have been fine, except for an upset stomach and a sore throat.

Even with commercial/public pools, the upper FC limit varies by state with Texas at 8 ppm and Florida at 10 ppm.

The recommendations on this forum have an active chlorine level roughly equivalent to 0.1 ppm FC with no CYA so less than 1/10th the level you might find in indoor commercial/public pools with no CYA. Most of the chlorine is bound to CYA and is for practical purposes inactive. It is held in reserve and released as needed, but the unbound chlorine that actually does the work killing pathogens, killing algae, and oxidizing bather waste (and swimsuits, skin and hair) is a VERY low level.

Thank you all for your responses and reassurances! I'm on board with the reasoning behind the chlorine level required. I'm a logical person (civil engineer), and I value empirical evidence and calculations. I just need to adjust my 'gut feeling' to account for updated information :). I really don't have a phobia - just a faulty basis, which has now been corrected.

So, from what BigDave said, and further discussion in the china shop, I have reluctantly concluded that my Nature 2 must go. I only say reluctantly because it's hard to see the $75 spent on the newly installed cartridge be worthless, but it can't be helped. I've never had my metals or calcium levels measured because I didn't think that it was important for fiberglass pools, but now I'm curious. I agree that it would be better to know what is influencing the pool chemistry rather having a black box that could be doing more harm than good, especially if it masks unsafe water by preventing the indicator (algae). At the very least, it doesn't change the FC requirement.

All that being said, I still need help with getting and keeping the FC level required. The pool is in full sun most of the day (96 degrees today and will be over 100 most of the summer) and the water was 86 degrees at the surface today. I usually add water every-other day to combat evaporation.

I measured FC at 0ppm last night, so I added 2 gallons of bleach at 9pm (18,000 gal pool). Today at 4pm I measured only 1.5ppm TC and FC. (TA 110 ppm, PH 7.5)

I'm guessing, based on the sun and heat and my current rate of consumption of FC, that I shouldn't try to lower the CYA of 80-90 ppm. Do you agree?

Then, if my goal is to keep the FC between 5-10 ppm for my CYA level, then what is the best way to do that? I was disappointed to see that the level was already so low by today, but I'm hoping that once I get it up where it needs to be that it will be easier to maintain. Did I not add enough last night or will I end up having to add that much every night?

Any guidance would be appreciated. Thank you in advance! I have a lot to learn, but I'm enjoying the chemistry so far :)

Ps- I'm using the Walmart hth 6-way test and also a Taylor drop kit (made for Leslie's pools - has R-0001, R-0002, R-0003 for FC/TC, R-0014 for PH, and R-0007, R-0008, and R-0009 for TA)

Once the CYA goes above 20 ppm, you can not successfully apply the BBB method using a DPD color match kit, or test strips.

Read the Best Guess page (link in signature) and get a K2006.