Let's talk about Alkalinity, Calcium and Magnesium in an SPS Tank

[capn_hylinur]

Originally posted by MCsaxmaster
Please do as I'm curious. Suffice it to say, things cannot be quite as you described above

lol--I think they were threads from you on magnesium-LOL

won't be the first time I interpreted wrong

[capn_hylinur]

Originally posted by MCsaxmaster
Please do as I'm curious. Suffice it to say, things cannot be quite as you described above

I checked back on this thread--on page six you wrote a great piece on magnesium---but this was not the thread.

I only have a modest background in chemistry, but usually I am not too far off on comprehending what I have read.

With your obvious fantastic expertise perhaps you can clarify "things not cannot be "quite as your described above"

I'll concede to "quite" as a very tactful way of remarking about this
and ask your help here in clarifying.

[cwegescheide]

One thing I notice is my PH is higher when my Alk is low.

[gary faulkner]

Originally posted by cwegescheide
One thing I notice is my PH is higher when my Alk is low.

I think that is a given, right?

[MCsaxmaster]

quote:
--------------------------------------------------------------------------------
Originally posted by cwegescheide
One thing I notice is my PH is higher when my Alk is low.
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I think that is a given, right?

No, with lower alkalinity the pH will be lower, all other things being equal. If pH here really is lower when the alkalinity is higher, then CO2 must covary with alkalinity in this case. Hence, the CO2 becomes significantly higher as alkalinity climbs higher, causing the reduced pH.

cj

[cwegescheide]

Originally posted by MCsaxmaster
No, with lower alkalinity the pH will be lower, all other things being equal. If pH here really is lower when the alkalinity is higher, then CO2 must covary with alkalinity in this case. Hence, the CO2 becomes significantly higher as alkalinity climbs higher, causing the reduced pH.

cj

Since my supplementation is provided by a calcium reactor I guess I buy that. My thinking was/is the amount of alkalinity supplied by my reactor is buffering my ph, not allowing it to rise above a certain point. EVERY time my ph goes above a certain point (just recalibrated my probe - it was reading 8.6 but I know its not that high) I know my Alk is low. Now I'm not sure if its because the amount of bicarbonate in suspension is low or its the lack of Co2 in the tank.. Since CJ is working on his MS in Marine Biology I will take his word for it

[gary faulkner]

Originally posted by MCsaxmaster
No, with lower alkalinity the pH will be lower, all other things being equal. If pH here really is lower when the alkalinity is higher, then CO2 must covary with alkalinity in this case. Hence, the CO2 becomes significantly higher as alkalinity climbs higher, causing the reduced pH.

cj

Sorry, I read that wrong. If my Ph falls I always check to see if the alk is lower. It has a direct relationship not inverse?

Thanks

[capn_hylinur]

Originally posted by gary faulkner
Sorry, I read that wrong. If my Ph falls I always check to see if the alk is lower. It has a direct relationship not inverse?

Thanks

that would be a direct relationship

[MCsaxmaster]

Originally posted by gary faulkner
Sorry, I read that wrong. If my Ph falls I always check to see if the alk is lower. It has a direct relationship not inverse?

Thanks

pH is positively correlated with total alkalinity and negatively correlated with total CO2. Raise total alkalinity, everything else equal, and you'll raise pH. Raise total CO2, everything else equal, and you'll lower pH. Raise both total alkalinity and total CO2 proportionally and you'll maintain the same pH.

These relationships ARE NOT linear, but understanding the general form of the relationships is very useful.