Using polystyrene

[Philip Altmann]

If I use polystyrene as the medium to grow my vegetables instead of gravel,  does the polystyrene float up and down in the flood drain containers or shouild it just stay at one level. If it stays at one level this means that the roots of the vegetables will be non immersed in  fish water. 

Can someone tell me which is the proper method?

 

 

Philip