Oil Like Film On Top Of Water?

Hi,
 
I've had a new tank setup for about 6 months now, and there is this oil like film that develops over the top, after water change and cleaning it all and the glass, it come back again about 1-2 days after cleaning. Any ideas what it is and how to get rid of it? Doesn't appear to be doing any harm, its just unsightly. 
 
[Images attached]
 

This is likely a protein bio-film, as it appears to be greenish, and streaky.  There is another that is whitish and more solid, caused by an iron bacteria.
 
The protein bio-film is likely caused by organics, and aided by still water (no surface movement).  It is harmless by itself, though it can thicken and reduce the needed gas exchange.  Some recommend paper towels, laid on the surface then carefully picked up, to remove it, but I find it easier to do during the water change; I simply invert the changer to pull water in along the surface.  Of course, it may return.  Increasing the surface water movement helps to prevent it or control it.  But I would also check into the organics.  This is much like cyanobacteria in this respect; regular substantial water changes, vacuuming the substrate, keeping the filters cleaned, not overfeeding, and not overstocking all help.
 
It is interesting that I have seen this in one tank for a spell, then it suddenly disappeared and didn't return for months.  There are surface skimmers that you can get for some canister filters, and I used these several years ago; they worked to prevent this, but small fish and fry kept getting sucked in, so I gave up and removed them.  I haven't seen this since, except in the one tank, but last for that one was months ago.
 
Byron.

I've had this too in my old Rio180 but it only appeared in one corner - the opposite corner to where my filter outlet defuser was ... I soon worked out that one filter wasn't moving the water enough and so this lovely film appeared where there was little or no movement. I tried all the things Byron has mentioned to get rid of it but in the end the only way to be rid of it for good was to buy a second filter and place the outlet defusers towards the centre of the tank. 
 
Now I've got an even larger tank I still run it the same way - two external filters in opposite corners with the outlet flow pointed towards the middle front ... this causes the flow to turn on itself and pushes the flow back toward the inlet pipe and also keeps the surface moving

I too, as above , have had this, and still have to a small degree in my discus tank. I used to feed quite alot of a,beef heart preparation I made myself, so I knew it had a reasonably high fat and protein content. There's less of a film now that I've reduced feeding that. As said, I put in place a small eheim surface skimmer. Main problem with that is it readily draws in any floating foods, such as Prima that I feed regularly. I switch it off to avoid this (just have to remember to switch it back on lol). Using a hose angled upwards to draw it off when water changing is by far the easiest way to remove some of it, I found the paper towel approach a pain , and I wa concerned about anything undesirable being released. As above, the main thing to avoid is a static surface which will greatly reduce the interchange of gases, oxygen being most important. I'm not clear on the chemistry of it all, but I think foods can cause it. I experimented with a few in a small clean tank, when moved around it soon appeared

Adding floating plants, reinforcing the filtration, increasing water surface agitation, adding snails, spreading paper towels/regular paper on the surface works well..

I recently learned that putting 3-4 drops of hydrogen peroxide per 2.5 gallons of water can help eliminate oily surface films the next day for about a week's time.

Dunno the effects on shrimps though but my snails and plants are doing just fine.

Thanks for all the info everyone, I've increased the surface movement and this seems to have helped a lot, some still clings around the sides but have manually removed as much as I can, its just comes back though, feeding is reduced as much as possible, and regular water changes. But it's management more now.

another tip would be - be careful of putting your hands in the tank too often. Our hands pick up greasy residues and if your putting your hands in the tank a lot we can transfer some of it