[BattlePope]

Hi,

I'm an oceanography student and am performing a research experiment to examine how changing water conditions (pH, salinity, temp, etc.) are going to affect phytoplanktons' primary productivity. Anyways, I'm doing pH first and we are lowering the acidity with HCl. I still need to figure out what to use as a buffer though. What would you guys recommend?  There will be phytoplankton/algae in this water when I lower the pH.

Thank you!

[hobobot]

what specific pH are you looking to be at?

[BattlePope]

I'm looking for the "breaking point" where the algae will be unable to produce anymore organic carbon (essentially a measure of primary productivity) so it all depends on what the algae can withstand. I have 3 tanks set up and for my first run I'm going to go pH of 8, 7.5, 7 and keep on moving down by 0.5 until I find this "breaking point". So to answer your question, I'm not really sure at this point but I can't imagine it going lower than 5-6.

[BattlePope]

*Ignore me, I am impatient*. Anyone? Urgent!! Any help would be MUCH appreciated!

Thank you.

[hobobot]

I'm having trouble thinking of one that won't hurt the little guys. You may consider consulting someone who knows a lot about brewing, as beer is usually kept at a lower pH.
Wikipedia also has a good list: http://en.wikipedia.org/wiki/Buffer_solution

Out of curiosity, why HCL and not H2SO4?

[BattlePope]

Why H2SO4 and not HCl? Were just planning on using HCl because that is what we had available...

[BattlePope]

Alright guys, I NEED to have this figured out by tomorrow. Can someone PLEASE PLEASE PLEASE let me know what acid/buffer combination would work best for this experiment?

[Borek]

It will be difficult to find one buffer ready to cover whole range, and changing buffer you add additional variable to the experiment. Perhaps something fancy like combination of tetrasodium pyrophosphate and citric acid could work, but I would not try to use it without earlier trying to find out how these things are done in literature.