Water hyacinth is pretty tolerant and needs little nutrient to grow (which is one of the reasons it's invasive throughout the country). The main thing you need for fertilizer is some form of nitrogen. A little goldfish or something would be adequate for that, and the other side nutrients would come along with the fish food.
The more sterile and non-leaching your substrate, the more nutrients will be missing from your aquatic environment. If you decide to plant anything in the substrate, you will require either a richer media under the gravel/kitty litter/etc. or an all-in-one fertilizer solution such as pond tabs.
