Is my skimmer doing its job?

[mididnitdragoon]

I have a bh 2000 reef octopus in a 75 gallon.
This what I get after three days

https://postimg.org/image/qrwuo6jdt/

[Skim]

Well I guess that depends on what is in your tank.

[mididnitdragoon]

i have:
2x clownfish
2x blue chromis
1x yellow tang
1x picasso triggerfish
1x diamond goby

also a mix of corals.

i try to do a weekly 10 gallon water change with rodi water, is this absolutely necessary?

[GimpyFin]

Looks like it's doing a decent job to me. Your skim in the bottom of the cup looks fairly dark so that's good.