I have the Midi flotor, its a simple design and is very effective. You want the water level to sit about 2 - 3" above the inside tube and adjust slightly from there.
Ensure you get the correct sized air pump to drive the airstone and replace the airstone asap. The ones that come with them are not brilliant.
Mine has been skimming away giving me a very dark skimmate. Very effective, most of my corals have seen improved colouration, improved expansion and improved growth since starting to skim.
No need to replace them IMO, very good skimmers.
I have also read today in my new bible that this type of protein skimmer does contribute to tank oxygen content as it creates a waterfall eefect.
The other advantage is that there is no power pump inside the sump or aquarium that will release heat into the water.
This is a big advantage during heatwaves like we saw recently as it is difficult enough to keep a tank cool in those conditions, which also deplete oxygen from the water and cause fish and living organisms to increase their demand for oxygen.
Hopr that makes sense.
I was talking about the aquamedic not the prism.