sjimmyh
Member
I am writing this article in the hopes that it will make it to the sticky board so anyone having problems in the future can read it. Seems there is a common lack of understanding regarding pH and alkalinity.
You decide for whatever reason you want to read about alkalinity as it applies to our aquariums. What you will most likely find is that Alkalinity is a measure of the tanks ability to resist a change in pH. Okay, you understand this completely and head off to work your tank thinking you have got a great understanding of what you just read.
Here is where things get whacky. Some people will set up the tank and find that their pH is low when they have ideal alkalinity. From what they read they know that a higher alkalinity tends to give a higher pH. They also read about pH buffers when considering addition to the tank and learn these buffers will raise not just pH, but alkalinity too. Everything seems to fall in place with your knowledge still. For many people, this knowledge is good enough. They find that for their tank they run around 8.3 pH with an alkalinity of 10 dKH (or close to 3.5 meq/l). Even though this data tells me that they have a problem with the tank, the problem is managable and since the aquarist was able to deal with it effectively and still be in the "ideal" range for both pH and Alkalinity he/she goes on about their merry way none the wiser.
Enter the other folks. They find that they can't seem to keep pH in the "ideal" range. They add buffer to raise pH and it does work for a short while. The next day they find themselves very close to where they were before adding buffer. So, what's the story?
Okay, here is where the complete understanding of alkalinity in our tanks needs to be understood. At least, if you want to correct the pH issue. Alkalinity and pH go hand in hand. Calcium is very closely related too.
What your book most likely didn't tell you about alkalinity is that a specific alkalinity should give you a specific pH under normal conditions. Even though they are not the same measurement it may help you to think that they are two ways to measure the same thing with respect to our tanks. I know of no synthetic sea salt that doesn't fall into this catagory when mixed so don't worry about that for now. Some salts are better at some things, but thats just us trying to get our tanks tweeked to ideality.
The following describes approximate pH in seawater for a given meq/l alkalinity: (dKH is just meq/l x 2.8) (2 meq/l = 5.6 dKH)
ALK pH
1.o 7.92
2.0 8.21
3.0 8.33
4.0 8.42
5.0 8.50
6.0 8.55
Notice that the pH increase per meq/l change goes down as alkalinity goes up. This will be important later.
There is one impurity that typically enters our tanks to mess with this relationship. That is Carbon Dioxide (CO2). CO2 forms carbonic acid when disolved in water and can throw this alkalinity to pH relationship off. Bottom line, if you do not have close to the pH listed for a given alkalinity in your tank then you are dealing with excess CO2. With high CO2 you would need a higher alkalinity than 2 meq/l to get an 8.2 pH.
Lets look at adding buffer to correct the issue. We add buffer which raises alkalinity and pH both. Temporarily, the problem seems solved and if you have a small CO2 problem small additions of buffer or alkalinity additive on a regular basis will permanently solve the problem. IF, you have sufficient CO2, it will not. Here is why.
Higher alkalinity levels tend to precipitate Calcium. Calcium is a pretty big part of alkalinity. By precipitating Calcium you actually lower the alkalinity. Confusing? Just think of there being a "cap" on alkalinity levels in your tank. If you go too high, the tank will balance itself back to lower levels. PH buffers raise alkalinity to raise pH. If you have a very low pH (read as high CO2) you will need to raise alkalinity a lot to get a big change in pH (remember that pH goes up less for a 1 meq/l change in alkalinity if alkalinity is already high). If you go too high in alkalinity, the tank balances itself out by lowering alkalinity back down. PH follows this lowering of alkalinity and you're suddenly back at the pH and alkalinity levels you started with. The only remedy to this yo-yo is to lower the excess CO2 in your tank.
I will write an article about this to follow. For now, understand that for a given alkalinity you should always get the same pH levels. If you do not (your pH is different than the chart I gave you above for the listed alkalinity), than CO2 is most likely the culpret. If you are victom to a large amount of CO2 in your tank then you may never be able to obtain an alkalinity large enough to give you an ideal pH due to the tank wanting to balance it all back out again.
I do hope this helps your understanding of alkalinity, at least with how it relates to pH, a little better.
You decide for whatever reason you want to read about alkalinity as it applies to our aquariums. What you will most likely find is that Alkalinity is a measure of the tanks ability to resist a change in pH. Okay, you understand this completely and head off to work your tank thinking you have got a great understanding of what you just read.
Here is where things get whacky. Some people will set up the tank and find that their pH is low when they have ideal alkalinity. From what they read they know that a higher alkalinity tends to give a higher pH. They also read about pH buffers when considering addition to the tank and learn these buffers will raise not just pH, but alkalinity too. Everything seems to fall in place with your knowledge still. For many people, this knowledge is good enough. They find that for their tank they run around 8.3 pH with an alkalinity of 10 dKH (or close to 3.5 meq/l). Even though this data tells me that they have a problem with the tank, the problem is managable and since the aquarist was able to deal with it effectively and still be in the "ideal" range for both pH and Alkalinity he/she goes on about their merry way none the wiser.
Enter the other folks. They find that they can't seem to keep pH in the "ideal" range. They add buffer to raise pH and it does work for a short while. The next day they find themselves very close to where they were before adding buffer. So, what's the story?
Okay, here is where the complete understanding of alkalinity in our tanks needs to be understood. At least, if you want to correct the pH issue. Alkalinity and pH go hand in hand. Calcium is very closely related too.
What your book most likely didn't tell you about alkalinity is that a specific alkalinity should give you a specific pH under normal conditions. Even though they are not the same measurement it may help you to think that they are two ways to measure the same thing with respect to our tanks. I know of no synthetic sea salt that doesn't fall into this catagory when mixed so don't worry about that for now. Some salts are better at some things, but thats just us trying to get our tanks tweeked to ideality.
The following describes approximate pH in seawater for a given meq/l alkalinity: (dKH is just meq/l x 2.8) (2 meq/l = 5.6 dKH)
ALK pH
1.o 7.92
2.0 8.21
3.0 8.33
4.0 8.42
5.0 8.50
6.0 8.55
Notice that the pH increase per meq/l change goes down as alkalinity goes up. This will be important later.
There is one impurity that typically enters our tanks to mess with this relationship. That is Carbon Dioxide (CO2). CO2 forms carbonic acid when disolved in water and can throw this alkalinity to pH relationship off. Bottom line, if you do not have close to the pH listed for a given alkalinity in your tank then you are dealing with excess CO2. With high CO2 you would need a higher alkalinity than 2 meq/l to get an 8.2 pH.
Lets look at adding buffer to correct the issue. We add buffer which raises alkalinity and pH both. Temporarily, the problem seems solved and if you have a small CO2 problem small additions of buffer or alkalinity additive on a regular basis will permanently solve the problem. IF, you have sufficient CO2, it will not. Here is why.
Higher alkalinity levels tend to precipitate Calcium. Calcium is a pretty big part of alkalinity. By precipitating Calcium you actually lower the alkalinity. Confusing? Just think of there being a "cap" on alkalinity levels in your tank. If you go too high, the tank will balance itself back to lower levels. PH buffers raise alkalinity to raise pH. If you have a very low pH (read as high CO2) you will need to raise alkalinity a lot to get a big change in pH (remember that pH goes up less for a 1 meq/l change in alkalinity if alkalinity is already high). If you go too high in alkalinity, the tank balances itself out by lowering alkalinity back down. PH follows this lowering of alkalinity and you're suddenly back at the pH and alkalinity levels you started with. The only remedy to this yo-yo is to lower the excess CO2 in your tank.
I will write an article about this to follow. For now, understand that for a given alkalinity you should always get the same pH levels. If you do not (your pH is different than the chart I gave you above for the listed alkalinity), than CO2 is most likely the culpret. If you are victom to a large amount of CO2 in your tank then you may never be able to obtain an alkalinity large enough to give you an ideal pH due to the tank wanting to balance it all back out again.
I do hope this helps your understanding of alkalinity, at least with how it relates to pH, a little better.
