green rocks

I've been "farming algae" on rocks in a sunny window for the otos. Put this one in and took a picture in the morning (before tank lights were on). The otos quickly congregated on it.

Before mid afternoon they had eaten almost all of it!

You can even see the strand of green poo one is already voiding.

I don't have enough jars of rocks to give this to them every day, or even once a week- have to wait for more rocks to grow it back. Makes me question if they're really getting enough off of tank surfaces. I wonder if I started putting zucchini or algae wafers in this spot, now that they're learning it's a feeding spot, would they figure out to eat off of it yet.