1)
Why is He called "Kel Sal'i"?
1.
Radak: In the past, He was my Rock and strong tower [to shield] from enemies.
2)
Why did he say "You forgot me"?
1.
Radak: In Galus [it seems that You forgot me].
2.
Malbim: Now there are waves, but we do not hear the voice of Chesed, and there is no miracle.
3)
What is "Koder"?
1.
Rashi: It is an expression of blackness, like "v'Kadar Aleihem" (Michah 3:6).