I have a penguin biowheel 150 hob, and a fluval FX5. Currently my stock is 3 red empress (3" each), 4 lemon jakes (3" each), and a bn pleco.
With that stocking the FX5 should be more than adequate. The Penguin 150 is more for a 30 gallon tank, I believe, so I'm not sure it's doing much good getting water movement at the surface, just not enough power IMO especially on a presumably 6' tank. If you want a HOB plus the FX5, I'd go for an Aquaclear 110 in the middle and then the FX5 intake one end and outtake the other end.
Before putting out money for that, though, I'd try adjusting where the return is on the FX5 to get more water movement. And consider taking the 150 off, unless there's a special reason you have it on there - I assume you upgraded to the FX5 and were seeding via the 150? You could put the 150 media in the FX5 and then you wouldn't need the HOB.
I don't usually have this surface stillness issue but I'm overfiltered on most tanks vs the manufacturer recommendation e.g. I have an Aquaclear 50 (200gph) on my 20 gallon long, an AC110 on my 55 gallon, and so on. I only see the oily film in my crayfish tank which just has an Aquaclear 20 powerhead and the output only stirs up about 1/3 of the surface, thus the film builds up on the other half.
Another option would be to add a Hydro V or similar sponge filter and the bubbles that pop and break the surface will help with the oily film. Not sure if you want the sponge filter in your tank though if it's a display tank for example, though you can hide it behind rocks, for example.
The major concern with the oily film, I believe, is that it can interfere with oxygen getting in and out of the water, which can be a problem especially if your filter dies due to a power outage, and definitely won't help you as you add more fish down the road (I assume).
