Water changes and carbon in the filter clear tannins real quick. Be careful with the water changes, if you stir the substrate you'll just get it all dirty.
Not much at all in my case. For a standard 10 gal w/ 1.5" of soil bottom layer, I crushed up about 1/4 of an egg shell's worth as fine as I could and mixed it in. The intent was to provide calcium long-term but honestly, I don't really know how it takes egg shell to decompose.Hey ItsDubC, could you elaborate on the eggshell? How much did you put in?