Whats your tank spec? light?
Looks like insufficient lighting to me. The rest of the head also not fully expended.
You shouldnt be able to see the gap otherwise.
my 2cents
Juz to say hi guys, new to this forum and is looking forward to learning from u all here.
Currently have a 6.5ft setup. juz finishing cycling b4 new year and stocking it up now.
"Ching Tuo Tuo Zi Ziao"