| | Re: Red Clay for Iron?? like laterite..
Using clay balls was a common practice years ago before plant specific substrates came out, mostly as a way to control release of fertilizer pellets wrapped in the clay. The iron in ferrosilicate clays is bound in the structure of the clay and won't be available to the plants. If you've already got soil in the tank chances are good that there's enough iron in there though, I wouldn't worry about it. Should you really want to add something for your crypts etc I'd recommend Flourish Tabs.