I wanted to put in a review after reading the other reviews. Imagitarium has a separate CO2 dual chamber that is required when using these tablets. It says recommended on the directions and I think this is something the manufacturer should correct on the packaging. The CO2 chamber is *required* for a safe introduction of CO2 into the system, planted only or not. Also not listed but 1000% required is a CO2 dropper monitor. These are teardrop or round glass orbs that suction to the side. The orb is filled with a liquid colored CO2 indicator. 4 stars because the tabs work with proper precautions but the manufacturer should be clearer on the requirements of properly monitoring CO2 levels somewhere on the packaging. In my opinion, there's plenty of space on the back of both the chamber and tablets for the instructions. Choice of wording cannot be stressed enough with these literal life-and-death items.

This does not do what it advertises. Not remotely. Not safe for fish, and will not provide increased co2 levels for any length of time.

Had a completely cycled 5 gallon tank. Added quite a few plants with one fish, one trapdoor snail, one rabbit snail, and little bladder snails. Followed the directions and placed one tablet in the tank. I woke up the next morning to find my fish dead. The suds were pouring out of the filter in the top. Way too much CO2 for anything that needs oxygen in the tank. I wish there was some sort of warning about this.