Water hyacinths are floating plants there require a LOT of very high lighting, therefore they should only be in outdoor ponds. In a home aquariums, they usually do not get enough light to grow healthy, not to mention they block the plants below from getting enough light. They have thick root masses that rot if the plants are dying from insufficient light. You may also get a mosquito problem because mosquitos love laying eggs among its fronds.
If you use them in ponds, they can grow well and fast and is a good absorber of nitrates.