have used OF CO2 tablets for a few days and here is what I have to say. It take one tablet around 12 hours to dissolve, the bubbles form around the tablet and near it end stage the tablet starts to break into pieces and float all over the tank. I prefer the excel since it is just a liquid and its effects are noticeable, second is Hobby Sanoplant since the tablet dissolves within a few minutes and the bubbles it releases look similar to that of a tiny co2 diffuser of a pressurized system. Last, OF CO2 tablet if you have no other choice. I only keep my lights on for 9 hours so the tablet remains undissolved when the lights go off.