Film on surface of female betta tank

Question

I recently took in one of my friend's male Bettas to treat it for ich (Ichthyophthirius infection). When I brought him back I noticed a film on the surface of her other Betta's tank (this one is a female). It's a small 2 gallon hexagonal tank with a mini filter, that is made for 1-3 gallons and has a very slow trickle. The same filter is powered by a pump that also runs a bubbler that she has attached by a T-valve, so both have little power. It is to my knowledge that Bettas, especially in small tanks, need little water movement due to the fact they naturally thrive in ditches and rice patties. However, what I saw made me a little concerned. Her tank has film at the top. I used her net and swiped up the film as best as I could. It wasn't sludgy, it was actually more clear, almost white as it became dry. I asked her about it and she said that only her female's tank does that. Her male is in an identical tank and he makes bubble nests all the time. She switched them from each having their own bowl to these tanks about 6 months ago and said her female's bowl had the film then, too.

I am familiar with the idea of a film being caused by a poor tank environment, algae, or not being clean enough, but her water is clear and her gravel looks clean too. I'd like to be able to recommend a fix for her if one exists, but I'm not sure if this is normal for female bettas. She has no live plants and no other fish or invertebrates in either setup, so I'm confused by there being a difference.

What could this film be? Is there a film that only females make, possibly for reproduction? Or is this a sign that maybe her tiny setup isn't doing enough? Or a mix of both?

Answer 1

I don't know a lot about bettas, so this answer is not complete.

A film on the water is an indication that something is not working optimally; it might be a protein film and the reasons for this can be one or all of these.

Waste from the food, waste from the fish, mucus from the skin of the fish, unfertilized eggs from the fish and the filter itself might produce proteins if the bacteria start to break it down.

No matter the reason, the film has to be removed manually as it blocks the gas exchange across the water-air interface.

Simply removing the film might actually be the cure just by increasing the gas exchange, so the water absorbs more oxygen and makes the biological processes run more effectively and the problem might never return.

Remember this is an answer but it might not be the answer, the film might be from fat/oil from the fish food, it might even be from the hands of the owner (I am not saying that it is), it might even be pollen from the outside of the house.

No matter what it is, it needs to be removed.

Sources:

• https://www.cuteness.com/article/film-top-betta-fish-tank

• https://nippyfish.net/2006/07/13/protein-layer-unsightly-surface-film/

• http://www.pangeareptile.com/forums/showthread.php?56559-Film-layer-in-my-betta-fish-s-tank