Looks like the water level in the sump was very very low (the green part), or the air outlet hole at the top was blocked which caused the unit to fill with air and push the water level down. So this is a good example of how different light levels, and different nutrient levels, affect growth.
The upper part was out of the water, and only got slight spraying or splashing as bubbles popped at the top of the green area. So it got very little nutrients from the water. And, since there was no water to reduce light, the light was the strongest there. So you end up with very orange slime growth that can be peeled off with your fingers sometimes. It still does filter well if you remove it before it gets too thick.
The lower part was in the water, so it got lots of nutrients from the water, and a bit less light because of the water. So you get dark green growth. Darker has more nutrients but blocks light sooner, so if you clean it sooner then you can get more filtering.
So all types of situations and growth can grow and filter well.
The upper part was out of the water, and only got slight spraying or splashing as bubbles popped at the top of the green area. So it got very little nutrients from the water. And, since there was no water to reduce light, the light was the strongest there. So you end up with very orange slime growth that can be peeled off with your fingers sometimes. It still does filter well if you remove it before it gets too thick.
The lower part was in the water, so it got lots of nutrients from the water, and a bit less light because of the water. So you get dark green growth. Darker has more nutrients but blocks light sooner, so if you clean it sooner then you can get more filtering.
So all types of situations and growth can grow and filter well.
