Second what Soul mention. pull down the sleeve of the tube to make ur water level IN THE SKIMMER
slightly lower, maybe at a level just at the start of the collection cup
Put a s
ponge on the sleeve to cushion the outlet flow from your skimmer so that ur tank water will not have too much microbubbles.
Lastly, your skimmer is producing foam and this is good news - its working but no dark gunk produced yet as its still new and ur water might still be clean.
also take note , for in sump skimmer, every time u dip ur hands in the display tank, the foam will readjust itself. So don't panic, this is normal
Happy CNY