Lower PH with carbonic acid

[robgurr]

If you bubble co2 through water is apparently creates carbonic acid which obviously lowers your PH, here they say that if you add carbonic acid to water is creates Co2 and H2o, surely this is a good thing for 2 reasons.
1, I am lowering my ph for Rams, discus etc.
2, I am providing my plants with Co2

http://www.newton.dep.anl.gov/askasci/chem99/chem99661.htm

[f-fish]

Not sure how you would want to add this to your tank in a controlled well regulated fashion since CO2 + H2O http://upload.wikimedia.org/wikipedia/commons/thumb/9/96/Equilibrium.svg/15px-Equilibrium.svg.png H2CO3.
You already have your fish that make use of carbonic acid during respiratory gas exchange.

Now if you are keen at adding acids to get CO2 and lower the pH check out the Söchting Carbonator it uses citric acid and this bell design is the reactor and diffuser.

Later Ferdie