Underpowered Pump - Scum

Hi all, I think i have a problem to which I know the solution is buy a bigger pump but I'm hoping one of you can tell me different.

I have a Aqua Vogue 245 ltr tank with a External filter. That is a Ocellaris 850. I set it up in May last year. It's understocked and well planted, including a good amount of floating plants.
Water test suggest PH 7.6 (seems to have dropped) Ammonia 0.25 (maybe less) Nitrite 0, Nitrate 40 (might be higher I find these difficult to judge) Gh 120 - 180 KH 180 -240. Those numbers are pretty stable

The pump has the option of a spray bar and a duck billy type end. I've tried both. Neither disturb the water that much. When I fitted the filter pump I did not cut the hoses down at all but there is not a lot to play with i.e. I could probably take 6" off each if I really wanted to.

Lately I have noticed a greasy film on the water and, if I delay the PWC much more than a week or so a green bubbly scum starts to occur at the surface. The fish seem fine. In fact I recently noticed I have a baby bristle nosed pleco which is growing well. (quite excited about it tbh)

So, my Qs are is it anyhting to worry about.?
Is it because the supplied pump isn't quite up to the job and I need something a bit more powerful?
Is there another reason?

Thanks

Congratulations on your baby BN. 
Mine had babies a couple of years ago and they were very cute. If you can get any pics of the baby I'd love to see it. 

Congrats too! Would love to see a photo of it.

Thanks for your helpful comments. I've taken them on board. I also decided to give the pump a good going over and I've improved the flow. A few weeks ago I watched a your tube vid called pimp my pump or such like by pond guru. He maintains most pumps are set up wrong and you should have 3 bits of filter material in the bottom tray rough medium smooth then as mcuh bio mass as you can in whatever trays you have above that. So, anyway i gave this a go and bought some more, recommended bi mass. But instead of taking out one of the filter pads I squeezed the lot. I've now re-doneit all with one less pad and the flow is much better and my spray bar is disrupting the surface nicely.
I may upgrade at some point anyway but I no longer feel the need to rush. I'll also go for the air pump now and watch the feeding regime. I do give them frozen food every other day and flake every day plus dried as well every other day.
Thanks again and I'll post some pics of the bay plec in mo.

I see you've told a number of people that it's OK to leave fish to fend for them selves for a week or so and that  it's probably preferable to risking a holiday block. I can see how that could be the case with my large community tank but I've ordered a auto feeder anyway but I also have a small 35lt tank with 8 small Endlers Live bearers / guppies.
Will they manage without feeding for a week? They're so small I'm worried they won't.

I've attached a picture of one of my baby bristle nosed as you asked for one last time. But also , a rather poor one of some of the enders. Ignore the black and white one he's made of glass.

Thanks

I had a collection of auto-feeders when I was commuting/away most of the week for work.
I felt that it would be ok to leave most of my gang for a week, but leaving them for 5 days a week, every week, for several months was not a good idea.
I found that the auto-feeders worked very well once I'd worked out exactly what I wanted, and my gang all survived while I was making the decision to relocate.
I agree that testing the auto-feeder for several days before is very useful so you can observe the dispensing & how your fish respond. I found that knowing it was working well was very comforting while I was away.