To sum up what the previous few posters said: You need a stable, non-reactive tank material (borosilicate glass and stainless steel being the ideal) to prevent cracking.
I don't use tank-killers myself, only because those flavors are a little too harsh for my tastes. A lot of what I say is based off of what I view as my version of common sense, having a little knowledge of reactivity, tinkering and amateur research. I'm the farthest thing from an expert that is extant on this forums and I spend a lot of time dragging things on and talking out of my ....
Take what I say with a bigger grain of salt than most.