Can someone explain this to me? I have two plants in my 20 gallon tank. Danios and tetras live in there. Do I understand this correctly? RO water has no minerals/salts. So if your tank was all RO water, the salts in the fish's body would diffuse through the fish's gills into the mineral-less water, and they would die quickly from malnourishment.... I understand you have to take care of minerals and hardness (I don't really understand hardness) So can someone explain this to me? I'll add SeaChem Equilibrium to add back minerals. Next, I read I have to control hardness (which affects pH?) or whatever with Acid Buffer and Alkaline Buffer. Can someone explain this to me? So the questions I need answered are: 1. What is my Desired GH meq/L? I need to know this to see how much seacchem equilibrium to use. 2. Does RO water have 0 GH meq/L to start out with? Again, this is for the equilibrium calculation of SeaChem's website. 3. Please just explain kh, gh, hardness, etc. to me as much as you can. I really don't understand it at all.... So I don't know how Acid Buffer and Alkaline buffer with help, be necessary, etc. 4. Are Seachem Equilibrium and Acid Buffer/Alkaline Buffer all I need to add to full treat RO water (prime too of course)? I want my pH to be around 6.8-7. Thanks everyone!