Is there a link between PH and DKH?

[HAWK44]

This is more of a curiosity question, but one that got me thinking after I got a PH controller and started dosing kalk - is there a chemical link between PH and DKH? Conventional wisdom, in my case, says that as DKH is consumed (along with other chemicals), the PH will drop, in turn telling the controller to turn back on and dose more.

Am I in the complete wrong line of thought for this? I am welcome to be corrected and learn about the links in chemistry in reefs!

 

[redfishbluefish]

You can not use pH for adding kalk or any alkalinity additive.

 

[Spare time]

Here is some stuff to read

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

reefs.com

 

[MnFish1]

This is more of a curiosity question, but one that got me thinking after I got a PH controller and started dosing kalk - is there a chemical link between PH and DKH? Conventional wisdom, in my case, says that as DKH is consumed (along with other chemicals), the PH will drop, in turn telling the controller to turn back on and dose more.

Am I in the complete wrong line of thought for this? I am welcome to be corrected and learn about the links in chemistry in reefs!

There is a relationship. Alkalinity acts as a 'buffer' to try to maintain a certain pH depending on the buffer used. pH is a measure of H+ ions. In your example - as alkalinity is 'consumed' - up to a point, pH will stay the same - until the buffering capacity is used up. The main determinant of pH is CO2 (Carbon dioxide).

 

[HAWK44]

You can not use pH for adding kalk or any alkalinity additive.

What would make you say this? I am more curious than anything. A lot of people use PH controllers for dosing kalk with great success.

 

[HAWK44]

Here is some stuff to read

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

reefs.com

Thanks for the article! The whole carbonate vs bicarbonate thing in chemistry is an interesting thing to me. I appreciate you taking the time to post it.

 

[redfishbluefish]

The largest impact on pH comes from carbon dioxide. So you have a party with a bunch of people in your fish room and your pH drops down to 7.7 from your guests breathing. Your system is going to start to dump kalk into your tank when your alk and calc numbers were just fine.

 

[MnFish1]

What would make you say this? I am more curious than anything. A lot of people use PH controllers for dosing kalk with great success.

I think most people do not use the pH Controller to 'dose' Kalk, but instead to make sure the pH is not going too high in the tank.

 

[redfishbluefish]

DOH! It just hit me. I've been bothered by the comment that people use a pH reading to dose kalk. I'm not aware of anybody doing this. HOWEVER, some people do use a pH probe on there kalk reactor to know when to add more kalk. Now that makes sense to me! So the pH reading in this case has nothing to do with monitoring your alk levels, but simply indicates when it's time to put more Kalk into the reactor.

 

[MnFish1]

DOH! It just hit me. I've been bothered by the comment that people use a pH reading to dose kalk. I'm not aware of anybody doing this. HOWEVER, some people do use a pH probe on there kalk reactor to know when to add more kalk. Now that makes sense to me! So the pH reading in this case has nothing to do with monitoring your alk levels, but simply indicates when it's time to put more Kalk into the reactor.

I'm curious now lol. Why would the pH of saturated Kalk 'drop' at all? I always thought it was time to add more when there was no more Kalk on the bottom??

 

[arking_mark]

pH/Alk/CO2 have a defined mathematical model. Gven any two of these parameters, you can calculate the third. This also means that your pH is determined by your tank's CO2 and Alk levels. It should be noted that the addition or subtraction of CO2 does not impact Alk levels. So essentially, in our Alk stabilized systems effective CO2 determines pH.

 

[MnFish1]

pH/Alk/CO2 have a defined mathematical model. Gven any two of these parameters, you can calculate the third. This also means that your pH is determined by your tank's CO2 and Alk levels. It should be noted that the addition or subtraction of CO2 does not impact Alk levels. So essentially, in our Alk stabilized systems effective CO2 determines pH.

I was hoping you'd pop in

 

[redfishbluefish]

I'm curious now lol. Why would the pH of saturated Kalk 'drop' at all? I always thought it was time to add more when there was no more Kalk on the bottom??

If it were me, I'd do just what you say....keep a slurry of kalk at the bottom of the reactor. But some prefer monitoring pH and when it drops below some number....I think it's up around 12.5....it's time to add more kalk.

 

[arking_mark]

If it were me, I'd do just what you say....keep a slurry of kalk at the bottom of the reactor. But some prefer monitoring pH and when it drops below some number....I think it's up around 12.5....it's time to add more kalk.

The issue with Kalkwasser is keeping it saturated. CO2 absorbed from the air will eventually form insoluble CaCO3 which acts as an accelerate for more CaCO3 and your slurry is no longer what you think it is.

So by monitoring EC (monitoring pH is not as effective) you can know when to add more kalk to your reactor (or clean it out and then add more kalk).

 

[Randy Holmes-Farley]

There are two ways the folks use pH in relation to limewater/kalkwasser dosing. I used both.

1. The first is to know that you are not driving the pH too high. If aeration is not strong enough, then the pH can readily get above 8.5. Mine did when my skimmer was taken out of service for a ferw months as an experiment.

2. The second is to know when limewater is running out or becoming less potent. I could easily detect when my top off went dry by seeing the pH drop lower than usual, and I knew it was time to refill my reservoir. I could also tell when it was not dosing for other reasons, such as a clogged delivery line or a fault of something else that was raising the water level in the sump.

It is theoretically possible to control dosing by pH, but it would not lead to very stable alkalinity unless the CO2 level in the home was unusually stable. Open windows that had been closed and bam, the alk will be dropping due to less kalkwasser dosed to attain the same pH.