Q: HC wrote,
There is a sludgy film on the surface of my 2.5 gallon betta tank. I’m not sure what it could be from but I’m worried it’ll make by betta sick. Even if it isn’t harmful I think it looks ugly and I’d like to know how to get rid of it.
A: I have to assume you are talking about the grayish/white protein layer that builds on the water’s surface every 2 – 4 days after a water change. It occurs in tanks that have little or no surface agitation and is believed to be made up of mostly organic compounds and dust. I get it in my bettas’ quarantine tank where I don’t run a filter or airstone.
The protein layer is not particularly dangerous. It may prohibit the exchange of gasses, cut out light that is needed for plants and is pretty ugly but since bettas surface for air it doesn’t pose a substantial threat. Like you, I personally think it’s hideous and usually take appropriate steps to remove it. The simplest method is to agitate the water, either by installing an air-stone or filter. Because bettas don’t care much for strong current, I recommend a small air-stone with adjustable bubble control. Protein skimmers, used in marine aquariums, are not necessary despite what some other aquarists may recommend. You can also manually remove it by scraping the surface with a paper towel, piece of paper or cardboard. The downside to this approach is that it’s hard to get it all, it’ll always come back and in a tiny 2.5 gallon aquarium the paper towels will suck up a lot of water.