ok time to clear up a misconception..... Sponges dont consume nitrates or phosphates directly.... they are filter feeders, they dont feed through direct absorbtion of chemicals from your water they trap little bitty specs of stuff *(phyto or zoaplankton if you will) and eat that. if your feeding phyto then that is probably why they are flourishing. I like sponges, they are definatly one of my favorite animals.