Are the Pool Calculator ranges set in stone?

[nolefan]

Are the pool calculator ranges set in stone or can they vary between pools? I am writing about a different pool than in my signature, so here are the numbers:

Free form, in ground, diamond brite finished pool (7842 gallons), with a SWCG. The current numbers are:

FC:17 (and dropping after having to shock it due to pool service neglected to detect a burnt out salt cell)
CC: 0
TA: 70
PH: 7.6
CYA: 80
CH: ? (not sure right now, ran out of reagent. but usually around 300)
Salt: 3100
Temp: 85 and going up (I live in south Florida with constant sun on the pool)

Accoriding to the pool calc, these numbers give me a CSI of -0.33. I noticed that by keeping my salt level at 3200 (where i want it) and my TA at 90, the CSI would be -0.15. This is much better. But having a TA of 90 is outside the recommended (IMPORTANT) level as stated in the Water Balance for SWG's article. Is there a reason why? Is TA @ 90 ok for this pool? Do they just vary like that?

Thanks for the comments.

 

[JasonLion]

Certainly nothing is set in stone, but it is worth trying to understand why the recommendations were set they way they were and what the tradeoffs are before you go changing them.

I'm assuming the pool you are talking about has a SWG. With a SWG raising CSI to -0.15 is certainly not better than having CSI at -0.33. The CSI inside the SWG is much higher than the CSI in the pool and raising CSI to -0.15 can easily lead to calcium scaling. Having CSI at -0.33 is not dangerous even in a plaster pool. Also, raising TA with a SWG will tend to result in rapid PH increases, which means more work and can lead to serious problems if you fail to maintain the PH and it gets too high.

 

[nolefan]

Ok, thanks for the info. But when the pool calc is set to use a SWG, Why does it tell me that it is corrosive at that level. Shouldn't it take that into consideration? So then what would be the best CSI range to keep a pool with a SWG in?

Kevin

 

[JasonLion]

It doesn't say corrosive at -0.33, it says potential to become corrosive (if it goes lower). With a SWG the tendency is for CSI to go up if it moves at all, so that potential is very unlikely to be realized.

I consider -0.25 to -0.45 ideal for a SWG. However, be wary of trying to optimize this kind of thing too closely. Levels change and CSI naturally moves around a bit. You aren't normally in trouble unless it gets way out of range and stays there for a while. Meanwhile micro-managing can lead to unnecessary chemical additions and wasted effort. Most people shouldn't be thinking about CSI at all. It is only really important if you are managing extremely high CH levels or trying to do a no drain acid wash.