Serendipity.
Watching the tank a couple of days ago, I noticed the surface film of flotsam building up and realized that my canister filter has no means to capture and process this slick. I further realized that at some point this could inhibit gas exchange and light penetration, so I started investigating options.
I have been planning a 20L homemade sump to place in the closet behind the tank. It's a bit involved since it needs to be wired as well as plumbed through the wall. The tank is not drilled and taking down a stocked tank for drilling is not something I want to do, so I was thinking about a siphon overflow box. However minimal, this would entail extra flooding risk so I was planning double siphons and a Bean Animal standpipe arrangement in case of blockage, and a float switch or optical level sensor to shut off the return in the event of siphon loss. Still, none of this would address my oil slick!
I started thinking about auxiliary surface skimmers and siphon pipe add-ons, and came across the Sicce Shark 300 protein skimmer which happens to take inlet water from the surface. I was planning on one of these for my sump already, but now mocked up the in-tank alternative placement. Not only will it fit unobtrusively in the back left corner of the tank without moving rocks or equipment (except one small move to a single powerhead), but it is black, which should fade right into the background, and low profile, so the cup will be (at most) barely visible above my tank from any seat in the room. Being Sicce, I'm hopeful it will also be silent. I will need to notch my lid, but that's a 10-minute task.
If this works out as imagined, it could solve my oil slick problem, help my high phosphate problem, and not be the eyesore that many HOB and in-tank skimmers can be.
I need to think some more about this, but it seems an elegant solution to some of my most pressing issues, and may eliminate my need for a sump altogether. Even if I eventually build the sump, I was going to use this very skimmer anyway, so unlike most of my mistakes, I won't need to lose the cost outlay of the skimmer.
What am I missing here?
The only big downside I can see is not having my sump project to work on over the winter!