Water should be changed at least weekly.
Do you have any pets left alone in the house...maybe they did something.

You might want to give the roots a bit of a haircut.

Why not check w/ the people who sold it to you &/or installed it for you?

In the meantime, I'd get some aquarium grade charcoal bits (at the pet store) & sprinkle some in the water to keep the yuck/algae down. That black water/bad smell is of concern.

I use the charcoal in my mixes & especially in water rooting small Houseplants so the water stays unyucky & has no algae (like 1/2 tsp of chips to a 3-5" pot).

I find that Dracaena sanderiana grow best in soil, not water.
Unless the $200 refers to some special aquatic set-up, I would transition the Dracaena to potting mix.

Josh