If you run a search on hydroponic fodder on EC and IR, you will find some older responses.
My own experience with hydroponics comes from friends who invested in a system to provide green forage to their alpaca herd. Their alpacas loved eating the fodder, however, the crias born the following year exhibited extremely stunted growth. All of them. They were and are still the size of standard poodles. It is bizarre.
They added at some point, an alpaca based vitamin and mineral package to their feeding regimen, but I don't think they tested their hay or fodder to come up with missing nutrients and what they needed to add. They simply bought this commercial product.
I'm thinking that the hydroponic grass is likely both extremely deficient in many nutrients because it is grown in ...water, not soil, what nutrients are there are very watered down(like magnesium is in spring grass) and the sugar content is in either the roots or blades, and could be higher than an IR horse could handle.
I"ve not tested the fodder, so all of this is conjecture on my part.
Not to mention the amount of work required to seed, water , and harvest the heavy pads of grass. Their basement is taken up with this, requiring humidity control, additional water heaters, lights, timers, etc.
Saline, MI 2003