Langelier Saturation index (LSI for short)

Jump to latest Follow Reply
P

poolteckie

0
In The Industry
May 12, 2018
24
BC
Hi,
Can anyone tell me ( the pool chem guys), if I should be using the LSI for double checking if the pool water is corrosive or calcifying?

My colleague at work tested one of the pools I service at work ( kinda did that behind my back) and said" your too low on alkalinity and we just replaced the pool furnace!! If you keep that up ( low alkalinity), you'll wreck the furnace!
The Alkalinity happened to be in the mid 70's. He insisted it had to be 80 or higher.
I told him: " Don't you ever use the LSI to check for corrosive/ scaling in your water??" He said: "No! We don't have time to do that!!".
I told him I purposely keep the ALK in the mid 70's because the pH lands and stay's pretty much pegged on pH of 7.5 ( don't have to do the extra work with MA)
I told him i review each customers water when I get home and use Pentair's online LSI calculator ( tis quick)
For the pool in question the pH is 7.5; Alk 75 ish. CH: in the 280's ; more importantly the water Temp : in the mid 80's. So if i remember, the LSI is pretty much near 0.00
But more importantly, am I right for doing the extra step using the LSI - to further fine tune the water balance?
I know the alk should be 80~120, ch 250~350, pH 7.2~7.8
Should i ditch the LSI ? Especially if they're worried the furnace will corrode?
 
Hmmph,
From what I've read ( from the link above) the LSI has nothing to do with corrosion on metal pipes...But rather corrosion on plaster, cement etc ( calcium products ) .
So, does Alkalinity play an important role, it by itself in 'metal' corrosion ( i.e metal pipes - pool heat exchangers)?
if the pH is 7.5 ( ideal balanced ) but the alk is too low or too high - will that corrode or ( scale?) the metal pipes??
I know the ALK has to be between 80~120 ppm but if the pH is stable around 7.5 with the ALK at say 50 ( or maybe less?) would that corrode the pipes / exchangers?
Now knowing does nothing for metal corrosion ( or not), is there a formula like the LSI - to calculate if it'll corrode ( or not ) the metal pipes/ exchangers?
 
The only thing that will corrode metal is low pH. Calcium scaling can still occur in pipes if the CSI gets to high, just like on the pool surface.

Btw, we often recommend keeping the TA lower around 50-60ppm when the pH tends to rise too quickly.
 
jblizzle said:
The only thing that will corrode metal is low pH. Calcium scaling can still occur in pipes if the CSI gets to high, just like on the pool surface.

Btw, we often recommend keeping the TA lower around 50-60ppm when the pH tends to rise too quickly.
Click to expand...

There I use the LS for calcium scaling or corrosion for pool surfaces only.
And as you say for pipes - to prevent calcium build up.
So if i go back to my original question. If I have a pH of 7.5 and the TA is in the 70's, I bet I'm pretty much spot on when it comes to pool heater metal corrosion?
My colleague is wrong when he said those numbers ( i just mentioned) are too low!! ( he said earlier). But I want to prove him wrong that pH7.5 and alk in the 70's is fine right?
thank you
 
pooldv said:
Those numbers are likely fine, also depends on CH level.

If you enter all of your test results in PoolMath, link at top of page, it will calculate your CSI to let you know if there is potential for scaling.

More here, Pool School - Calcium Saturation Index (CSI))
and here,
Pool School - Calcium Scaling
Click to expand...
I always use the Trouble Free Pool Calculator!!! Its awesome!!! It taught me a lot of chemistry.
This is good news !! Since my colleague sneakingly checked one of my pools for a client and gave me (explicit) over it!
He said" We just put a new Pentair gas heater and your readings are too low!! " he angrily ranted.
The readings where (wow!) pH of 7.5! ( how is that corrosive? I argued back). And he said the ALK was too low! (really?).
The ALK being 78??? too low?? I kept the CH at around 280 ish ( knowing the water is warm 86F) i had been using the LSI for that - which is why its at 280.
But now thanks to you guys, LSI does not apply to metal ( pipes, heat-exchangers, boilers etc).
Thats a relief to here this !:kim:
It would be fun to know tho, just to what point the pH and ALK ( if applicable ) has to be, to starting munching away at the metal pipes
And get this, for a guy ( my colleague ) who gave me heck (embarrassing me), told me that : TC - FC = CC. He said I had that wrong!! Like HUH??
And i guess he doesnt know simple Algebra either ! : FC + CC =TC , if you move those variables around. And he said he's been doing pools for decades !!

I always look up to you guys for help!!
 

Enjoying this content?

Support TFP with a donation.

Give Support
I see that the CSI is set to -0.6 and 0.6 as corrosive and calcite build up but for pool surfaces only, like pebbles, plaster etc.
As in the previous post, the LSI or CSI doesn't calculate for metal pipes and boilers.
But a pH of 7.5 ( weither the Alk is high or low with a pH of 75) wont harm the pipes I take it ? As i've read in previous post?

- - - Updated - - -

oh yeah. i see it now. :)
 
my colleague who had said a pH of 7.5 @ ALK of 70 ~ 80 is too low for pool furnace ( we now know he's wrong on that now) said that : CC + FC = TC is also wrong ( i dont think he has any math education)
if you do simple math: TC - CC = FC or TC - FC = CC ( simple baby algebra ). He gave me heck on the TC - FC = CC when i told him that, but i guess he's also wrong on that too!
 
pooldv said:
Yes, pH below 7.0 is corrosive to metal regardless of the alkalinity.
Click to expand...
Perfect!! when he took a sample of water from one of my customer pools and made me test the sample in front of him. He flipped when he saw the ALK of 70's even tho the pH was a perfect 7.5!
Now I can tell him he should go take a pool course before ranting on to me about the ALK must be 80 to 120 or else damage to pool furnace.

I really want to thank you for looking into that.
From the sample i told him the CC's were around 0.2. He asked me how i got that reading ( testing me to see if i knew how to do it).
I told him : TC - FC = CC ( TC when you add the R0003 making a deeper red in the FC sample - if there are any CC's in it).
If the FC sample gets a more intense red then you take that reading minus the first reading before adding the #3 reagent equals CC ( i.e FC 4 , TC 5 ; TC - FC = CC ; 5 - 4 = 1 ; CC = 1.0 ppm. Time to shock)
He then freaked out and yelled wrong!! he said the darker red ( after adding the R0003 drops) 'is' the CC's.
So now he's wrong on 2 counts:
count 1: pH of 7.5 @ alk of 70 ~ 80 corrodes furnaces or is susceptible to corrode.
count 2: TC-FC = CC . Where he states FC ---> 5 drops of R0003 = CC ( he's wrong on that too, its supposed to be 'TC' he's looking at after adding the R0003 and not directly 'CC'.) you have to subract the 2nd reading from the 1st to get CC's).
 
Get a better test kit. All that color matching makes for large errors.

Order a TF100 test kit
The only other real option for a test kit is a Taylor K-2006-C. Be careful comparing prices because the K-2006 comes in sizes, designated by a letter. The basic K-2006 has .75oz bottles. You need to get the K-2006-C to get the larger bottles that you want. Even then it is a little short on the reagent & powder for the FAS/DPD test.

I also have the SpeedStir. It makes testing much easier.
 
mknauss said:
Get a better test kit. All that color matching makes for large errors.

Order a TF100 test kit
The only other real option for a test kit is a Taylor K-2006-C. Be careful comparing prices because the K-2006 comes in sizes, designated by a letter. The basic K-2006 has .75oz bottles. You need to get the K-2006-C to get the larger bottles that you want. Even then it is a little short on the reagent & powder for the FAS/DPD test.

I also have the SpeedStir. It makes testing much easier.
Click to expand...

Yeah I want that SpeedStir
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply