Yes. The openings are 4" x 42" and submerged. There are two scrubber chambers.
The fish can swim up into the chambers to feed and I can control their access by purging the vertical containers.
Basically, this is my lazy solution to creating a "grazing grounds" where I can control access without physically being there.
I'm still considering whether to make it a conventional waterfall scrubber that I can flood to feed, or an updraft bubble scrubber where it's usually full of water with air bubbles allowing algae to grow preferentially. I talked through it in the scrubber forums too.
In the case of an updraft skimmer, the bubbles act as a barrier curtain to keep the fish out while the algae grows. And I still have the option to purge.
The third (more aggressive) approach is to use the surge as the algae growing mechanism. This would actually be simplest (so might try it first). The idea is that my filling and purging, the media is exposed to water and air to act as a scrubber without needing a dedicated source of either water or air. The old original scrubbers were all classic surges (like Carlson) but algae like bubbles so it was a good fit back then.
I've seen inverted tanks where fish swim up before so that idea isn't new. But using it to create an algae farm with controlled access is (as far as I've seen). Most inverted tanks are permanently filled.
Having the tanks empty regularly also limits bacteria from taking over.
Ok... I also do think it's cool to have the fish swim up a vertical wall for feeding time... it's like a whole second tank that uses the sunlight that would be wasted against the wall.
Combined with the dropoff on the other end and the dark zone under the false floor, it would have four separate reef sections...
The shallow coral reef
The deep dropoff reef (ok, it's only a foot deeper but that counts
)
The dark caverns (sponges, no big fish access)
The algae meadows (vertical scrubber surge)
The penalty of these raised tanks is that my sump had to double in size to accommodate all that water in case of a total shutdown. It's more like an internal kiddie pool.