Yes the sand seems to darken a bit under where bacteria were eating, that might be the nitrogen, although it doesn't seem to spread over the rest of the sand, n

Yes the sand seems to darken a bit under where bacteria were eating, that might be the nitrogen, although it doesn't seem to spread over the rest of the sand, not sure if the plants are getting it. Also you need to keep adding bacteria because the keep dying off. They don't have the mobility to find all the dead algae, so they are gone pretty quickly.