As there are no fish in that system, the need for filtration is far less - I doubt that there is any mechanical filtration on the system at all.
@Ryanbrs mentioned adding some
Bio Spira, so there is biological filtration at least.
This is a coral propagation tank only - so it's biggest downside would be that it couldn't support any fish. The upside, of course, is that it's a very simple system with very little to go wrong. About the only thing I see right away that I would personally change (assuming I wanted to build such a propagation tank) would be to use a second heater.