Hello all! got a DWC system going with some herbs in it. dill, cumin, chives etc. The first cycle of 2 weeks was fine. After changing the water for the second cycle it got a strange odor a day later. i couldnt tell what it was but it slowly dissipated and the plants continued to grow. I am using the Perfect Start starter sponges as my grow medium surrounded by hydroton.

The smell is gone now and the roots are growing but the sponges are completely coated in thick rich green sludge. The water smells fine and has no residue in the reservoir. Some of the hydroton has the green on it as well.

I started with 2-3 seedlings in each cell and eventually thinned them out. Could this have produced enough dead matter in the system to make all this green sludge only in the sponges?

Could it just be a result of the nutrients sitting at the top of the water for a bit too long and absorbing into the sponge?