I have an aquaclear 110 in my 55gal I guess medium planted tank. Every few days I put a small dose of liquid ferts of iron and magnesium and such. Usually anything that looks halfway decent at Petco but going to use Excel next. In my filter is the sponge, bio bags, and a carbon layer. I thought I saw somewhere that the carbon will remove minerals such as iron and magnesium from the water. Am I just wasting my money by using liquid fert and carbon filters?