[Marky_sparky]

I am working on a personal  project for my aquarium to better control the pH.  I am going to build a pH probe that will continuously monitor the water in my 30 gal (113.56235352 L) aquarium.  My desired pH is 7.2.

Lets say that when the probe is in the water it reads a pH of 7.6:

I know that:  pH = -log[H⁺]
to determine the concentration you re-arrange the above to look like: [H⁺] =  10^-pH

therefore [H⁺] = 2.512x10^-8 mol/L
                [OH^-] = 3.98107x10^-7] mol/L

to achieve a pH of 7.2 the [H⁺] must be: 6.30957x10^-8 mol/L
which means my water needs an [OH^-] of 1.585x10^-7 mol/L

My question is: How do I calculate how much Acid to aid to get to this point??
I am using http://www.seachem.com/Products/product_pages/AcidBuffer.html which is a dry chemical.

[pear]

I think we would need to know the chemical properties of the acid and aid in order to even address this.

[stewie griffin]

This may be jumping ahead a bit, and it may show that I don't know much about fish...
Can you safely assume the pH will stay at 7.2 once you get it there? What about CO2 from the air working its way into solution, or perhaps the waste from the fish could change the pH?? It seems to me that what you really want is a nice buffer with it's pH close to 7.2.