For small tank, weekly 30% to 50% of water change will do and already reset your tank back to the basic requirement water parameter. Your observation are much more important than those test kit outside there.if u feel additional supplement are needed, just use the recommended minimum or basic dose from the product you intended to use.phosphate remover is a must even thought your po4 reading is zero because it will buffer your po4 rise in case over feeding your fish.