PH based on KH and CA

[Big Ray]

Hello all,
is there a formula or something to figure out what the natural PH under normal conditions and HIGH surface agitation should be based on tested KH and CA and MG ?

I see alot saying that on forums and in my own experience other elements such as even K+ effect the PH a bit, so just wanted to make sure/.

for example if my CA is at 400 and KH at 11 DKH what should be my PH ?

now if CA at 420 and KH at 6.5 DKH ?

I run Zeovit system and keep my KH at 6.5 DKH, which to many is too low to be able to keep PH !! which makes no sense to me. please advice.

any ideas are appreciated hopefully Boomer will clear this up a bit more

 

[redsea reefer]

Boomers post in this thread might help...

http://www.reefsanctuary.com/forums/reef-chemistry-forum/63746-ph-problem.html

 

[Big Ray]

Boomers post in this thread might help...

http://www.reefsanctuary.com/forums/reef-chemistry-forum/63746-ph-problem.html

thank you, but Im aware of co2 and o2's effect on PH, hence why I said "natural PH under normal conditions and HIGH surface agitation "

lets say the water sample is outdoors, with a HUGE air pump bubbling like crazy ...

I see many post saying for example " with CA of XXX and KH of YY you should have PH of xx.zz !!!!!" this makes no sense to me, as there are atleast 70 other elements in seawater affecting PH ! but there must be something on the net these ppl are basing their replies on ..


thanks.

 

[redsea reefer]

I see many post saying for example " with CA of XXX and KH of YY you should have PH of xx.zz !!!!!" this makes no sense to me, as there are atleast 70 other elements in seawater affecting PH ! but there must be something on the net these ppl are basing their replies on ..


thanks.

You're welcome Ray!

I have never seen a formula like this that people base CA of X + Kh of Y should = Ph of Z.

It doesn't make sense to me also because every tank is different with different factors at play...

I'm sure Boomer will have the answer though.

 

[Boomer]

Ray

is there a formula or something to figure out what the natural PH under normal conditions and HIGH surface agitation should be based on tested KH and CA and MG ?

Of course, we just finished with a calculator that does that But Ca++ and Mg++ do not make-up part of such an equation as they have no such function in such an equation. It is just temp, Saintly and Alk PLUS room air CO2 or what CO2 level there is outside.


Equilibrium pH Calculator

There are some cool new toys I just posted on the other day on the same question. You can not buy indoor Humidity, barometric pressure, and now yes CO2

$ ~ $120

Indoor Air Quality Monitor Temperature RH CO2 Meter - eBay (item 190459066012 end time Nov-19-10 22:48:01 PST)


No price yet

ZyAura -- products -- ZG106; ZG106A-M; ZG106A-H


~$183

Wall Mount Indoor Air Quality Monitor - Temp, Rh, CO2 - eBay (item 350408310508 end time Nov-27-10 08:01:52 PST)


as there are atleast 70 other elements in seawater affecting PH !

Nope pH is a pure function of Alk, CO2, Salinity and temp.

thank you, but Im aware of co2 and o2's effect on PH

O2 has not function on pH

 

[Big Ray]

Ray

is there a formula or something to figure out what the natural PH under normal conditions and HIGH surface agitation should be based on tested KH and CA and MG ?

Of course, we just finished with a calculator that does that But Ca++ and Mg++ do not make-up part of such an equation as they have no such function in such an equation. It is just temp, Saintly and Alk PLUS room air CO2 or what CO2 level there is outside.


Equilibrium pH Calculator

There are some cool new toys I just posted on the other day on the same question. You can not buy indoor Humidity, barometric pressure, and now yes CO2

$ ~ $120

Indoor Air Quality Monitor Temperature RH CO2 Meter - eBay (item 190459066012 end time Nov-19-10 22:48:01 PST)


No price yet

ZyAura -- products -- ZG106; ZG106A-M; ZG106A-H


~$183

Wall Mount Indoor Air Quality Monitor - Temp, Rh, CO2 - eBay (item 350408310508 end time Nov-27-10 08:01:52 PST)


as there are atleast 70 other elements in seawater affecting PH !

Nope pH is a pure function of Alk, CO2, Salinity and temp.

thank you, but Im aware of co2 and o2's effect on PH

O2 has not function on pH

Boomer, THANK YOU ! that answers alot of my questions.

I have been reading yours and Randy's posts for many many years now, I feel like I know you already haha so special thanks

So now claims that you see on the net saying CA or K+ effect equilibrium PH are not true, as they dont effect it directly, but they could effect KH, which in turn will effect PH. makes better sense now. the calculator is really nice, I will play around with it a bit to get the formula (just relations) and Im sure I will have some more questions for you soon regarding this.

thanks again.

 

[Boomer]

These are the pH equations

HCO3 - = CA / ( 1 +2 pK2 / pHt )

CO3-- = CA x pK2 / ( pHt + 2 pK2 )

CO2 = CA x pHt / [ pK1 (1 + 2 pK2 / pHt ) ]

pCO2 = CA x pH / [ pK1 s ( 1 + 2 pK2/ pHt ) ]


pH ( as tank pH / pH nbs) = [ pCO2 pK1 s Ѓ ( pCO2^2 pK1^2 s^2 + 8 CA pCO2 pK1 s pK2 ) ] / 2 CA




Ѓ = Square Root of ( ........)



s = CO2 solubility in mmol /atm, @ x Temp(C) and y Salinity where s is
s = e^ (pl1 +(S x p2)) henrys_coeff is the solubility of CO2 in moles/(l * atm).



p1 = -58.0931 + 90.5069 x (100.0 / t) + 22.2940 x log(t/100.0)

p2 = 0.027766 + ( -0.025888 x (t / 100.0)) + (0.0050578 x (t / 100.0)^2)

S = salinty
t = temp in K




pCO2 = ppm CO2

CA = TA - Borate Alk in meq/ l

TA = Total Alk in meq/ l

CA = Carbonate Alk in meq/ l




pK1 (as 10^-pK1) = 3633.86 / T - (61.2172 + 9.6777 ln (T) - 0.011555 S + 0.0001152 S^2 )

pK2 (as 10^-pK2) = 471.78 /T + ( 25.9290 - 3.16967 ln (T) - 0.001781 S + 0.0001122 S^2 )




pHt (as 10^-pHt) = pHnbs (as 10^- pHnbs) + log ( fH )

fH = 0.739 + 0.0307 S + 0.0000794 S ^2 + 0.00006443 T - 0.00117 S T

S = Salinity in ppt

T = Temp in Kelvin

 

[Boomer]

So now claims that you see on the net saying CA or K+ effect equilibrium PH are not true, as they dont effect it directly,

Yes

but they could effect KH, which in turn will effect PH.

But you can no go by that. If I fart in the water it will affect it also Of course, if the dKH is 12 dKH and I dump in a bunch of Ca++ in the tank so it is 600 ppm the dKH and Ca++ will go down as may the pH, as you are making "cement". We could say what about the mass of plants sucking up CO2 raising the pH or the mass of fish lowering the pH from shoving out CO2. You MUST look at it as a glass of water you are testing. K+ has not effect either directly or indirectly on pH. Ca++ is another issue, as I said above, if it is to high it may precip CaCO3. So, yes, we do want a balance so the equilibrium is not affected or say a safe range. You DO NOT want something like a pH of 8.5, 500 ppm Ca++ and 12 dKH because the tank will be a snow storm of CaCO3.


CA

Try to re-frame yourself from that and use Ca, Ca++ or Calcium as CA = Carbonate Alkalinity (true)

CA = TA - Borate

 

[Big Ray]

thanks

this answers my first question very well, I always wondered why my PH wont reach 8.3 at KH of 7 (borates not excluded) and temp of 80 salinity of 35, the normal PH is 8.1. I think this is why zeovit and Alexander G. dont worry about PH . even BRS salt has KH of 7 !

I get reading of 7.7 indoors ! so I guess some co2 Issues are present. (makes sense as windows are all closed.) and 8.0 outside, which can be related to borate in water giving me false KH readings (Elos) and excess CO2 of city air. so at least now I dont have to worry about reaching PH of 8.3 cause its impossible

now off to secondary questions I had about this

 

[Big Ray]

So now claims that you see on the net saying CA or K+ effect equilibrium PH are not true, as they dont effect it directly,

Yes

but they could effect KH, which in turn will effect PH.

But you can no go by that. If I fart in the water it will affect it also Of course, if the dKH is 12 dKH and I dump in a bunch of Ca++ in the tank so it is 600 ppm the dKH and Ca++ will go down as may the pH, as you are making "cement". We could say what about the mass of plants sucking up CO2 raising the pH or the mass of fish lowering the pH from shoving out CO2. You MUST look at it as a glass of water you are testing. K+ has not effect either directly or indirectly on pH. Ca++ is another issue, as I said above, if it is to high it may precip CaCO3. So, yes, we do want a balance so the equilibrium is not affected or say a safe range. You DO NOT want something like a pH of 8.5, 500 ppm Ca++ and 12 dKH because the tank will be a snow storm of CaCO3.


CA

Try to re-frame yourself from that and use Ca, Ca++ or Calcium as CA = Carbonate Alkalinity (true)

CA = TA - Borate

HAHAAHH lol makes perfect sense, thank again I will use CA++ now on.

 

[Boomer]

8.3 at KH of 7

It is not going to with a dKH of 7 and a Salinity of 35 ppt but more like 8.2 max and that is if the tank is outside At a indoor pH of 7.7 you have craps load of indoor CO2 or tank CO2 or a combo of them both.

Alexander G

I know him well He is in "our" book I helped out allot on by my best friend Tony Vargas that Julian Sprung will be printing soon " The Coral Reef Aquarium" . It is posted here.

 

[Big Ray]

Appreciate the Formula it has helped clear things up alot in my head.

now thinking about this last night, I started thinking if we could derive formulas for calcification, or basically with given KH, and PH (so co2 and salinity and temp and altitude) can we derive a MAXimum for CA++ concentration before the mixture becomes unstable, given we supply 3.25
times the CA++ level in Magnesium ? or are there other elements/variables involved ?

or maybe Im thinking too much too late at night lol I Willl try to look over my chemistry books from univ tonight to see if I can find anything.

 

[Boomer]

That is all here Jay


CO2SYS : Program Developed for CO2 System Calculations
ORNL/CDIAC-105

 

[Big Ray]

Oh wow, you are just amazing thanks again

looks like I have a long night ahead of me again