new salt chlorinator system

[PoolDoc]

My SWG (Aquarite) recommends a CYA level of 60-80 (80 being ideal). So keeping CYA at 80, 5% of that results in a recommended FC level of 4. This is lower than recommended on the "Best Guess" chart (Best Guess chart says min FC of 5 at this CYA level).

Could you clarify this for me? If I can keep FC at 4, this will save some wear on my salt cell (which is a good thing considering the cost of replacement cells!

Sorry, I had a response here that was a result of not fully reading what you wrote -- the rule about ASSUMING was in full force. But, let me try again.

There are two sets of recommendations -- besides my own Best Guess -- that I need to address here.

First, the SWCG manufacturers have lined up behind the old industry standard recommendations, which they've tweaked a bit, to raise the CYA level, but otherwise left unchanged. For example, Hayward's Aqua Rite manual suggests an ideal CYA level of 80 ppm, and a FC level between 1 - 3 ppm. It was this set of recommendations that I thought (because I hadn't fully read your post) you were asking about. And it's nonsense. If you follow it, and fail to use a supplemental algaecide, you will have problems.

They (the pool industry generally) are wrong; we (BBB method folk) are right. And, more specifically, the SWCG makers are borrowing a BUNCH of trouble for themselves, in the form of dissatisfied customers by following these dumb recommendations.

But, there's another issue.

TroubleFreePool.com -- I think; I'm not quite sure where it came from -- has promoted a percentage based adjustment of FC levels, including the 5% rule. The idea of a simple percentage based rule is a good one, IF it works. The problem is, it doesn't. I'm not sure why: it may be that the range needs to be higher. Or, it may be something else.

But, just to take a real world example: I have been servicinga pool, that has CYA = 100 - 120 ppm, and was being cleaned up from some algae on the walls, and in some leaf piles that had resulted from holes in the mesh cover. The water was crystal clear. To kill the algae, I'd raised chlorine levels to 30+ ppm (30%), and it was mostly dead. However,chlorine levels had dropped from 15 - 20 ppm 3 days ago, to 10 ppm yesterday morning. And, mustard algae had begun growing rapidly!

Now, let's summarize:

+ Intial state: pH 6.8 - 7.0; FC 5.0; heavy algae on walls and under leaf piles
+ 3 - 5 days ago: pH 6.6 - 6.8; FC: 40 ppm descending to 20 ppm; algae dead on walls and dying in leaf piles
+ 2 days ago, AM: pH 6.6 - 6.8; FC 10 ppm -- RAPID (overnight) mustard algae growth
+ 2 days ago, PM; pH 7.4 - 7.6; FC 40 ppm -- slow mustard algae death
+ 1 day ago: pH 7.4; FC 25 ppm -- continued slow mustard algae death
+ This AM: pH 7.4; FC 25 ppm -- continued slow mustard algae death

Looking at it through the percentage model: the pool accumulated HEAVY algae (non-planktonic) at FC = 5% of CYA or HIGHER; it cleared at at FC = 40% of CYA, but over days, not hours. It began to RE-GROW at FC = 10 - 15% of CYA.

Richard (Chem_Geek) has done me, the PoolForum, TFP, and pool owners as a whole, a HUGE service by combining the work of a number of lab chemists, into an analytical model that can be applied to pools. That's a GREAT thing, and one I value highly.

But, I'm much less enthusiastic about the assumption that many seem to make (I'm not sure Richard does this) that this analytical understanding of the CYA / Chlorine relationship FULLY explains what's going on in pool chemistry. The CYA/Cl relationship is a PIECE of the puzzle, but it's FAR from the whole puzzle. I could run this post on for pages, listing un-answered questions I have about pool chemistry. And, I am 100% sure that that list would omit many important questions . . . because I don't know to ask them.

So, while I'm fully convinced that Richard knows more about the analytical aspects of swimming pool chemistry than anyone else in the world, that does NOT mean I believe Richard yet possesses (or is likely to possess in my lifetime) a full and complete analytical model for the chemistry and microbiology of swimming pool. And, until we have a full analytical model for swimming pools, we have to use an empirical model, that combines what we can learn from the (partial) analytical models, with what we can observe.

MY observation is that my Best Guess values are more likely to 'work' most of the time, than the 5% rule is.

That doesn't mean the 5% rule won't work for you! Precisely because we do NOT have a full analytical model, we often see things happening in pools, that we do not understand. A perfect analytical model would always predict what would happen in YOUR pool. The fact that we (BBB proponents) have a BETTER model than the pool industry as a whole does NOT mean we have a perfect model, or even a good approximation of a perfect model.

So, we have to fall back on real world observation. Our recommendations are just that: recommendations.

But the 'acid test' is, does it work?

If 5% works for you, GREAT! But, it's not what I recommend.