For what conditions?
Duckweed and algae will consume ammonia before it even becomes nitrates as can some other water plants.
Water chestnuts do well in the heat too.
Bananas, and Lufa are a couple hot weather plants I know that will use up lots of nutrients.
Tomatoes, cucumbers and corn are greedy warm weather crops
The broccoli and other cabbage family are fairly greedy cool weather crops
and under alkali cool weather conditions I know water cress will use huge amounts of nutrients.
Bamboo can use a fair amount of nutrients year round in the right climate.
Well Bananas and bamboo are probably the only ones completely unsuited to floating in a raft.
Water chestnuts you could skip the raft and simply use some gravel to anchor them in some plant pots down in the bottom of the raft trough.
Watercress might do better on some form of floating mats instead of a blueboard foam raft.
I am trying to find out if there is a type of corn that does not grow very tall???
A strong comfrey tea will stunt verticle growth.
When I grew some popcorn the stalks didn't get very tall. Of course the squirrels ate it all before we could harvest any.