[Disciple882542]

different types of situations may call for both. For example,

if you don't evaporate an adequate amount of water to replace it with enough Kalk to adequately sustain the Ca/alk levels in your tank you might need both.

Also, if your pH consistently runs a little low but your caclium demands are high you might need both as well.

Just my .02.

God bless,
disciple