Oily Surface Water

Hello all,

I have a 10 gallon tank with 1 male betta (very healthy) and 1 awesome amano shrimp. They get along well. Tank is mostly sand with a strip of gravel. 1 piece of driftwood, 2 anubias plants, 1 nice amazon sword and 1 moss ball. Aquaclear HoB filter with sponge, carbon and bio media.

I have not tested the water. The tank has been up and running for 2.5 months now and the media came from another filter of a cycled tank. Bio load is small for the tank and as stated before, betta is very healthy and active, lots of bubble nests and the shrimp has molted 3 times (that I know of) and is huge.

Still I keep getting and oily looking film on top of the tank that disperses if I dip my finger in but seems to be constant unless I let the water level get down lower than I would like. I assume the added water agitation keeps the oil slick from forming and I could add an air stone to see of that helps but there must be an underlying bacteria concern? I have Googled the issue and it sounds like a film of bacteria.

Do I actually need a heavier bioload? Perhaps the beneficial bacteria have or are dying off because of low ammonia and nitrites?

I would prefer to stop the underlying issue rather than resorting to extra surface agitation that my betta may not like.

 

What's your substrate, what kind of sand?

 

It's probably not "sand sand". I wanted black sand so I got a bag of black "sand" from petco or petsmart and it's very much just finely crushed gravel. Definitely not what I consider sand. If I didn't want black (makes it easier to find the shrimp) I would have gone with pool filter sand.

Honestly can't remember the brand off the top of my head.

 

It is biofilm. I would get an air stone to agitate the surface of the water. It will help.

What sort of filter do you have?

 

It's a biofilm that will usually occur for a couple reasons, a high level of organics in the water and not enough surface agitation. Some people will remove it with paper towels (skimming the surface with one) or by using a cup (submerge most the cup and allow just a tiny stream from the surface to flow into the cup). Either method can work but has to be done frequently.

The film itself is harmless but can reduce the air exchange that allows co2 out and oxygen into the water. A permanent solution is easy though, make sure you're staying up on your filter maintenance and/or add a power head or bubbler to the tank to agitate the surface. Also you want to be sure that you don't have a low spot or a corner somewhere in the tank that is collecting detritus, regular gravel vacs usually do the trick. With sand you can hover your syphon over those spots to suck it up or I personally in my tanks that are heavily planted will use a piece of dowel (could use a spoon or something too) and swirl it around to lift it up from the substrate as I syphon out the water.

Hopefully this helps! I had a betta tank that I struggled with biofilm constantly for a long time, just a thin film but super annoying in a display tank. I finally got the flow from my power head right through the tank to get and keep it off. The low flow needed for a betta tank can make it a bit tricky sometimes so you will want to be sure to address any organics and filter issues before you try increasing flow rates in the tank.