CluelessInNY
Aquarium Advice Activist
Not sure what it is, but it's clear to the eye until you see it from a side angle with the tank lights. The stream from the powerhead makes a "dent" in it (think of a stream flowing into a lake in winter where the lake is frozen, but the flow from the stream makes a bulge of unfrozen water into the lake)
Is this what a protein skimmer eliminates? Is this a problem?
Is this what a protein skimmer eliminates? Is this a problem?