Apparently it is, but there are different kinds. I went and bought some but when I got home and read the instructions, in addition to it removing chlorine it mentioned something about providing a "protective coating" for the fishes scales. That made me a bit nervous as I don't think I need a "protective coating" blocking nutes from the roots I shelved it and stuck with letting the water stand for 24 hours. I am interested as well to hear the responses to this one.
Yeah you have to be carefully because some of these work with sodium, which is bad for plants unless in trace amounts, and some of the other ones have chemicals that bind the metals in the water, which is not good for someone trying to grow MJ