I've tried 2 different brands. Both seem to work. The only bad part is that if you don't use all of the water that you've added that stuff to, you can't wait and use it the next day----by then it's turned the water nasty------trust me on this one! So now I wait to add the 'good bacteria' to the water, until after it's in the tank. (Then I don't waste any.)
I've used them on every tank i've had in the past 5 years, prior to that i did it the old way. I've never had a problem with those type of bacteria in a bottles and will use it on this 180 i'm setting up now. It does work.