well im no hydro guy but something sounds wrong with air pump(there is one in those right? not just a water pump). either not running often enough or at all. if its just a water pump you gotta keep that moving or it will do exactly what it did and stagnate or form algea etc. also looks like the plant isnt getting enough light or it isnt close enough. just my thoughts fortunately there are some real talented hydro growers here so youll get your answers.