Help me understand PH vs KA

[jimmy_c]

Its been a long while since my HS chemistry class so need help understanding this relationship.

I know PH is the measure of Hydrogen ions. For out tanks anything below 8.0 our tank is more acidic and anything above 8.3 its more basic. So we attempt to stay with in that range. Seawater is about 8.1

 

Using API test kits. At a TEMP of 78.8 Here's what my tank measured.

PH -- 8.0 -- 8.2 Lights have been on for 3 hours (Color is so (*&^%) hard to read.)

Kh -- 179 which has been holding there for the past 5 day. (thats when I got the test kit)

 

I know PH fluctuates with lights off and on. Not sure what it drops to at night. So here's my question.

1) Does PH affect the Kh. If so how?

2) Is KA the same a alkalinity?

3) The reason we "buffer" is to stabilize the PH so the swings are not as wide.. (which I do not buffer). Should I buffer? what indicators should I be watching to determine if I need to add some buffer.

 

Like I said I don't have a full handle on this and looking for some of you wizard help me understand.

 

Thx All !!

[HarryPotter]

Its Kh (Alkalinity), not KA

 

Heres a GREAT article and resource on the relationship between Kh and PH

 

http://www.advancedaquarist.com/2002/5/chemistry

[Nano sapiens]

I believe that the OP is reffering to 'Ka' (aka: 'Acid Ionizoation Contant').

 

http://chemwiki.ucdavis.edu/Physical_Chemistry/Acids_and_Bases/Ionization_Constants/Calculating_A_Ka_Value_From_A_Measured_Ph

[Benny314]

Firstly ditch the API test kits, they are notoriously inaccurate.

Also not sure on KA, normally API kits have KH (carbonate hardness) and GH (general hardness) tests. It's the KH one that's important as that is the alkalinity measurement and alkalinity is needed for corals to encrust and grow (corals will absorb alkalinity out of the water making it drop).

[Circle_City_Bill]

The carbonate and bicarbonate ions in the water create a pH buffer. The pH is determined (to a large part) by the ratio of the two ions (and not the absolute concentrations of the ions). So two solutions with the same alkalinity can have essentially the same pH. Buffered solutions are not absolutely resistant to changes in pH, but generally do not exhibit large swings when acid or base is added to the solution. The alkalinity is a measurement of the concentration of the basic ions in solution (again, largely carbonate and bicarbonate)...and represents the buffering capacity of the solution. Alkalinity can be lowered as coral precipitate calcium carbonate to build skeleton, or by neutralization by the acidic components of the dissolved organic compounds in the water. And, changes in CO₂ concentrations due to photosynthetic cycles and fluctuations in atmospheric CO₂ can cause changes in pH by changing the concentration of carbonic acid in the solution.

[Hig789]

Yeah I agree with the above. Ditch the apo and get a ph meter and the 10 and 7 calibration fluids. Randy, the guy who wrote that article that Harry linked is a reef chemistry wizard. Search for some more of his articles and I'm sure you can find what you are looking for.

[spinycheek]

Don't feel bad, the pH/CO2/Alkalinity relationships are horribly complex and change depending on temperature, mineral content, atmospheric pressure, etc. So pH affects alkalinity, but alkalinity also affects pH.. . Luckily, most reef systems can be greatly simplified and we can get by with just keeping a few parameters in check. Your Kh (alkalinity) being in the correct place is the most important part in regards to maintaining pH. Alkalinity creates a more stable pH environment that also permits corals to calcify correctly. Just add alkalinity and pH should fall in line. My favorite has always been to use baking soda, but one can use many other ''buffering'' options out there to achieve the same results.

[jimmy_c]

WOW Outstanding link Harry. My LKF store was telling me to "buffer". I wanted to understand why. Think I have a better handle on it now. Last week I had the LFS check my KA. The reading was off the chart BUT my water sample sat in a hot Texas car for two hours I bet the temp was between 90 to 95 degrees. So I figured that reading was false. The test kit give me a general idea of my PH but I would like to be a little more accurate about knowing what it is....

 

So how much are PH meters an could someone recommend several..

 

Again Thanks All... :0)

[Hig789]

This is what I have. Can't comment on the others though. This one is completely waterproof and will float. It also has 3 calibration points.

 

Haha. Sorry my dumbass forgot the link. It's kinda expensive but I'm sure there are cheaper options out there I just can't comment about on them because I haven't used them.

 

http://www.dakotainstruments.com/mobile/product.aspx?ProductCode=WD%2D35634%2D14&gclid=CLHH7qqtpMcCFYU6aQodcoQKCA

[HarryPotter]

WOW Outstanding link Harry. My LKF store was telling me to "buffer". I wanted to understand why. Think I have a better handle on it now. Last week I had the LFS check my KA. The reading was off the chart BUT my water sample sat in a hot Texas car for two hours I bet the temp was between 90 to 95 degrees. So I figured that reading was false. The test kit give me a general idea of my PH but I would like to be a little more accurate about knowing what it is....

 

So how much are PH meters an could someone recommend several..

 

Again Thanks All... :0)

Glad you liked the article.

 

Salifert tests are the gold standard- here's is the link. At only $14, it's a great option.

http://m.marinedepot.com/products/sf1135/salifert-ph-test-kit

 

in all honestly, once you get your parameters (Ca,Mg,KH) in line and steady you won't have to test your PH often. Most tanks (including mine) balance out perfectly if they are in a normal location (Not too stuffy with CO2) and are maintained