disc1
-RT * ln(k)
You cannot infer alkalinity from pH like that. You certainly cannot infer calcium levels.
Kalk Dosing
- Thread starter jrok3401
- Start date
You cannot infer alkalinity from pH like that. You certainly cannot infer calcium levels.
The realtionship between alkainity and pH is not that direct at variable CO2 levels as they occur in a reef tank. CO2 drives the pH but does not affect total alkalinity.
CO2 is often higher or sometimes lower in the water of a reef tank than standard athmospheric levels( around 400ppm).
The CO2 level in the water at a given point in time depends on a number of things including: the CO2 level in the air around the tank ,the rate of gas exchange via surface agitation/aeration, CO2 production by bacteria and other respiring organisms, CO2 reduction via photosynthesis.
The amount of CO2 in the water changes the pH but not the total alkalinity There are plenty of tanks with pH 8.4 with low alkainity and plenty with high alkainity and low pH.
This article has a graph of pH vs alkalinity for a given level of carbon dioxide:
http://reefkeeping.com/issues/2004-09/rhf/index.htm
Raising the alkalinity will raise the pH, but the difference is fairly small in the 7-11 dKH range, and carbon dioxide can lower the pH far more dramatically than that.
http://reefkeeping.com/issues/2004-09/rhf/index.htm
Raising the alkalinity will raise the pH, but the difference is fairly small in the 7-11 dKH range, and carbon dioxide can lower the pH far more dramatically than that.
I know it's hard to explain and takes a while to understand. Many folks have trouble with it.
This may help or make it worse:
CO2 in the water drives pH.
The level of CO2 in the tank varies due to room air levels and exchange rates between the room air and the tank .
CO2 can be produced and consumed biologically in the tank too.
Higher or lower CO2 levels do not affect total alkalinity .
CO2(carbon dioxide) +H2O(water) gives you CO3 (carbonate) plus 2 H+ protons. .
The extra 2 H+ lowers the pH.
One of the 2 added H+ protons joins the new CO3 (carbonate) which has 2 units of alkalinity making CHO3 (bicarbonate) which has only 1 unit . So, at this point alkalinity is plus 1 from a new bicarbonate ion.
The other new H+ proton joins another carbonate ion already in the tank and changes it from(carbonate) CO3 which has 2 units of alkalinity to bicarbonate(HCO3) which has only one unit of alkalinity for a minus 1 alkalinity .
The net result is H+ is plus two, alkalinity = net zero.
This may help or make it worse:
CO2 in the water drives pH.
The level of CO2 in the tank varies due to room air levels and exchange rates between the room air and the tank .
CO2 can be produced and consumed biologically in the tank too.
Higher or lower CO2 levels do not affect total alkalinity .
CO2(carbon dioxide) +H2O(water) gives you CO3 (carbonate) plus 2 H+ protons. .
The extra 2 H+ lowers the pH.
One of the 2 added H+ protons joins the new CO3 (carbonate) which has 2 units of alkalinity making CHO3 (bicarbonate) which has only 1 unit . So, at this point alkalinity is plus 1 from a new bicarbonate ion.
The other new H+ proton joins another carbonate ion already in the tank and changes it from(carbonate) CO3 which has 2 units of alkalinity to bicarbonate(HCO3) which has only one unit of alkalinity for a minus 1 alkalinity .
The net result is H+ is plus two, alkalinity = net zero.
Some people note the pH dropping during a big party at their home. 
Syntax1325
Acro Addict
Some people note the pH dropping during a big party at their home.
Yep! I had house guests on a cold winters weekend, ph dropped from 8.2 to 8.0..... Several hours after they left the ph was back to 8.2.
fishresponse
New member
Some people note the pH dropping during a big party at their home.
Jokingly I tell people to limit their breathing or go outside for deep breaths
Limewater(aka kalk,calcium hydroxide) is used as top off in lieu of other alkainity supplements or plain fresh water. It won't mess with salinity that wy; it adds calcium and hydroxide . The hydroxide binds with CO2 to add CO3(carbonate alkainity). As top off it continuously adds a balanced amount of calcium and alkalinity and raises pH since it uses CO2. If one uses a pH controller to turn it on and off it can lead to salinity issues related to a lack or excess of timely makeup water additions to cover evaporation.
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AcroporAddict
There is no substitute.
To the OP: I've never really felt like keeping pH at a certain level was really necessary. As long as your KH is at an acceptable range, you should be OK. Randy's pH article states an acceptable pH range in a reef tank is 7.8-8.5 with calcium levels at 400 or greater.
http://reefkeeping.com/issues/2007-05/rhf/#3
In other words, if you keep your alkalinity and calcium in range, and you don't have some other issue driving your pH lower or higher than Randy's recommended range, then why bother chasing pH numbers?
Is you tank outside the 7.8-8.5 range to start with? You did not post where your pH is at and what tank pH you wish to achieve. No sense in seeing a problem if there is not one to start with.
I wasn't the OP but, I did have the question about using a kalk reactor to maintain a certain pH range. I put the reactor on line originally, and pH went up to the 8.5-9 region. It got me worried about it going even higher so I put a program in my apex that would shut down the top off/reactor if ph got above 8.5. After a few days, my sump began to run low due to evaporation and the high pH. I then incorporated a second pump to switch on and bypass the reactor at times when the pH was above 8.5. It was more of a temp solution to buy some time while I figured things out. Since then, I have lowered the value to 8.3. Today numbers are as follows.
PH. 8.3
DKH 8
Calcium 500 (it has always ran high)
Salinity 1.027
Although I feel those are good numbers and things have remained stable for a week now, I am in the works of doing a kalk reservoir and pumping kalk in with a medical doser much slower and taking the reactor off line. I think that even though it has worked for a minute or two, in the long run it will not.
PH. 8.3
DKH 8
Calcium 500 (it has always ran high)
Salinity 1.027
Although I feel those are good numbers and things have remained stable for a week now, I am in the works of doing a kalk reservoir and pumping kalk in with a medical doser much slower and taking the reactor off line. I think that even though it has worked for a minute or two, in the long run it will not.
The pH of the whole system generally shouldn't have gotten to 9 unless you were measuring close the the addition before it mixed thoroughly, adding too fast (more than 0.5-1% of the tank volume in less than an hour or two), or you were dosing milky limewater. Were you doing any of those?
AcroporAddict
There is no substitute.
How old is your pH probe, and when was the last time you calibrated it? Sometimes it is the equipment and not the tank. For me, 99% of the time my tank stays within certain ranges for pH, maybe 7.9-8.0 as a low after the lights have been off all night, to a high of 8.35-8.45 after lights have been on for several hours. If I see a deviation from this pattern, first thing I do is check my equipment, which includes calibrating the pH probes.
Just saying you could have a probe that is bad or needs calibrating just as easily as you could have an actual chemistry issue. Good to rule out the easily fixable things first. I tend to replace my pH probes every 12-16 months.
