Need? no. There are many additives that you might decide to add but I would not say they are required.
This is coming from someone who would love to sell you something. I sell lots of additives and they have a purpose, but I have set up far too many tanks that receive no additives and simply get regular water changes to say you need to add anything.
Here is the rub. On nano tanks, it is very easy to maintain a tank with water changes alone. my 12 gallon desk tank gets 5 gallons changed once a week and I get great results. On a 120 or 200 gallon tank, this is just impractical. Changing this much water is more difficult and more expensive than relying on additives and filtration to handle the bulk of the filtration and supplementation.
On a 20 gallon tank, you can get really far with water changes alone.
