film like stuff on the water surface of shark tank

Recently noticed there's a weird sorta colored film like substance on the surface of the water. Can't be seen without a flashlight at night. Any ideas? Ammonia & nitrites are basically zero, but nitrates were high so did a decent sized water change the other day & used extra Prime.

I would first think that this film is the result of protein breakdown. It happens in saltwater as well (hence the use of protein skimmers).

Another cause could be from oil or lipid emulsion from foods. The oils used in processing food could accumulate as such, and I have seen light oils do this.

Putting paper towels (unused, clean) on the surface will wick it up

Do you have an airstone, or any air-operated gizmos, in this tank?  Bubbles usually break up the surface enough to get rid of the film.  If not, a filter that draws some of its intake from the surface will skim it off.  Eheim makes...or made...a handy little gadget for their canister filters that did just this and worked well.  If you use a sump, set up one of the overflows with a little hole at the surface and it will draw this stuff off as well.

The gunk is still in your water; you just won't be able to see it anymore.  Out of sight, out of mind...

I've also had the misfortune of watching my lovely wife peer into my tank, comment on a floating bibbit of some sort, and then casually reach in to remove it. I was standing at just the correct angle to see a giant circle of multicoloured oily film radiate instantly outwards from her fingers when they briefly touched the water. We then had an extended conversation about sunscreen and other skin lotions with particular attention paid to a future lack of such potions coming in contact with my aquarium water.

jjohnwm wrote:I've also had the misfortune of watching my lovely wife peer into my tank, comment on a floating bibbit of some sort, and then casually reach in to remove it.  I was standing at just the correct angle to see a giant circle of multicoloured oily film radiate instantly outwards from her fingers when they briefly touched the water.  We then had an extended conversation about sunscreen and other skin lotions with particular attention paid to a future lack of such potions coming in contact with my aquarium water.

Hilarious. Betcha you didn't tell the wife ...