need is a big word and you dont need any the only ting you need is to add calcium and alk now you can choose any mehtode to do it and IMO they are all good
2 part product very good and easy to dose but have to be dose each day
and cost a harm and a leg if you have even a medium bioload
kalk reactor , cheap to run but need a lilte investment , will keep you parameter well and need lilte maintenance
calcium reactor expensive to buy cheap to run need very litle maintenance
and will keep your parameter as well
Hard to choose
