Hi everyone! I'll say it from the start that I'm not knowledgeable with chemistry but I'll call for anyone's help in making me understand this simple reaction. I'm interested in finding out what reactions are occurring when CO2 is dissolved in water. The scope is for my hobby which is aquariums. In planted aquariums we dissolve CO2 as a macro nutrient for the aquatic plants. The side effect of doing this is that the pH of the water drops. To prevent it dropping to dangerous levels we often put bicarbonates in the form of baking soda. What I noticed is that a high enough level of bicarbonates might also reduce the concentration of CO2 in the water if that's correct. I'm assuming this as the fish do not show signs of CO2 poisoning as it was the case when low levels of bicarbonates were in the water. I'm using reverse osmosis water in my aquariums so the pH is not buffered unless I put bicarbonates in. So far I managed to understand that CO2 + H2O <=> H2CO3 <=> H+ + HCO3- <=> CO3 + 2H+ Also, H2CO3 is a weak acid, in water it should quickly dissociate to H+ + HCO3- (if my understanding of the above equilibrium is correct) making the pH go down. If we add more bicarbonates into the water it will shift the equilibrium H2CO3 <<=> H+ + HCO3- thus buffering the pH. Lack of bicarbonates will shift the equilibrium H+ + hCO3- <=>> CO3 + 2H+ plummeting the pH. Am i talking none sense? Or at a "moron" level I got things right? Many thanks for your help!