[Blacktetra]

Alright, so I'm aware of the typical approaches to removing that rainbowy-whitish surface film. The answers (ranked by how often suggested) that I've seen are:
Greater surface disturbance using filter outflow.
Surface disturbance via air stone.
Surface skimmer (though many people say these are useless for freshwater tanks, some posts I've read seem to suggest otherwise)

I'm sure there are other methods, BUT...
I'm not interested in removing it! I want to know what it is, and what it does.
The reason I'm asking, is because I know it's bacteria, that it's eating something in the water, and must need air since it only seems to appear on the surface. I also know it can block gas exchange between the water column and the environment.

But does anyone know anything else?
The name of the bacteria? What it eats? What it produces?
I can't find much info on it, and I would like to study it.
I'm considering getting two glass vases, putting a single blade of micro sword, or a java fern plantlette in there, and giving both of them the same nutrients, only one vase I'll wipe the surface each morning, and the other, I won't, to see what results I get.

 

[bsherwood]

I have it from time to time on my 40. I put h202 in a small spray bottle. One that provides a very fine mist seems to work the best. I spray the surface and that seems to knock it back nicely.

 

[c9bug]

Surface skimmer (though many people say these are useless for freshwater tanks, some posts I've read seem to suggest otherwise)


...The reason I'm asking, is because I know it's bacteria, that it's eating something in the water, and must need air since it only seems to appear on the surface. I also know it can block gas exchange between the water column and the environment.

I just wanted to point out for other readers that surface skimmers work great for fresh water tanks. Protein skimmers, however, are only useful for saltwater tanks.

Are you sure that oil slick is bacteria? I was always under the impression that it was a byproduct of the decomposition of plants/animals. I especially notice it if one of my fish dies, all the oils just collect at the surface.

Now I'm really curious as to what exactly oil slick is as well.

 

[Virc003]

It is not bacteria. It is is organic waste from bacteria in your tank and/or all the reasons mentioned by c9bug. Snails will eat it too.

 

[Darkblade48]

It is not bacteria. It is is organic waste from bacteria in your tank and/or all the reasons mentioned by c9bug. Snails will eat it too.

Some claim that the film is a result of eisenbacteria.

 

[discuspaul]

It's a protein film built up by the bacterial sub-structure of decomposing organic wastes. It collects on water surfaces for oxygenation to maintain itself. Mainly caused by uneaten foods, decomposing plant matter & other waste sources. Not harmful to aquatic life and not difficult to control & remove through various means.

 

[rhiro]

If this is a result of decomposing organic wastes then would this indicate a need for a water change to bring down the organic waste content?

 

[discuspaul]

If this is a result of decomposing organic wastes then would this indicate a need for a water change to bring down the organic waste content?

Absolutely.
Large & frequent wcs do indeed have the effect of bringing down the organic waste content in tanks, thus producing better water quality and conditions, but they also thereby aid in ridding the tank of protein films, and replenish the healthy mineral content of tank water which gets depleted though usage by plants & fish.

 

[rhiro]

Thanks @discuspaul. Never thought about the oil slick in respect to organic waste content.

 

[Straight shooter]

Bacteria are there, but the film is made up of other things. At the water-air interface of natural water bodies, material accumulates to form a surface film. Surface films are altered by sunlight, water movement etc. The films are basically microorganisms and organic matter.

So, it's a natural process and nothing bad. It can inhibit gas exchange (O2/CO2) at the surface somewhat but that's about it.

I get it when I overfeed a little. That seems to be the trigger in my setup.

 

[Wilderman204]

One of my Flag Killifish figured out he could eat it. After a day he cleared almost all the biofilm from my 55gallon lol. I just increased the flow near the surface and it doesn't form anymore. Without good flow, my dirted tanks get a lot of surface scum during their first few months.

 

[Blacktetra]

Lots of good info so far. Thanks to everyone's help. Still curious what kind of benefits or drawbacks it might have. I think the proposed experiment may still be of interest.

 

[Kubla]

I have a cheap surface skimmer and it works well. I have it connected to an inline pump that goes to my CO2 reactor. Just a few minutes after starting it the first time the film was gone in a few minutes.

 

[flight50]

Just to reiterate what c9bug and kubla said, surface skimmers work well. Not all are made the same of course. If anyone says they don't work well for FW tanks, stop taking advice from that person. A protein skimmer is what they are thinking of and it is a totally different piece of equipment. Just because it has the name skimmer in it, does not warrant that it is a protein skimmer by default. I love my little Eheim skimmer. The down side to them though is that they do clog fairly quickly. I have to clean my filter sponge every 3-5 days. I get lazy with it sometime and just wait til my weekly water change.

 

[Blacktetra]

so answers so far are: bacteria, waste from bacteria, proteins, all of which I would think are correct. I'd imagine it begins with waste, or proteins and bacteria colonize the food source, and in the process generate waste.

What I find interesting in my own case, is that it BEGINS as an oil sheen. You know, rainbow colors, swirl with the current, etc. but later grows pale, and eventually becomes a white, thin, opaque solid that looks dry on top. When I collect it by wiping it out with a paper towel it will crumple up and look kind of like dried up saliva.

I've found that a particularly high dosage of glut doesn't seem to affect it. Though my dosing is relatively rough (bottle says 1ml/10 US Gal, mini tank is roughly 1/3gal, roughly 20 drops per ml, = 2 drops per gallon so roughly 1/3 gallon should be getting less than 1 drop.) I've doubled, and even quadrupled the amount used and haven't seen a noticeable change in the stuff. In it's color, or speed of growth.

 

[roostertech]

I find that adding an airstone in clear mine up real fast.

 

[nchmi28]

This thread is exactly what I was looking for. 2 days ago I sectioned off a small area of my tank, reducing the flow to feed the fish in. Well today when I went to feed them there was a film over the water in the section. I was trying to figure out exactly what it was and if it was harmful. I also sectioned off the area to put floating plants in (once I get them) It makes sense that feeding in an area with no flow would cause increased bacteria buildup in that spot.

 

[Shaythesalmon]

Right now, all of my snails are at the surface eating it. I tried to cut down the amount I was feeding my fish and frog so maybe it's starvation food?