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Freshwater Aquarium/iridescent film on betta tank


Ihave a 2 1/2 gal tank with heater and filter. I have a Betta  and keep his tank clean. Feed him small amount each day and take any droppings out each day. I treat new water with Aqueon Betta Bowl Plus and small amount of Aquarium salt.  I have noticed an iridescent film on top of the water. Want to know what it might be and is it dangerous to him   He seems okay-active- no visual sickness. His tank is acrylic and the heater lies at the bottom of the tank.Don't know what other info you may need.  Rebecca

Hi Rebecca

You did not indicate what type of filter you have, but that film occurs in smaller tanks when the filter is not strong enough to circulate the water and agitate the surface. To my knowledge, the film is harmless to fish. The best way to eliminate the problem is to get a 5 gallon tank with a hang on back power filter. The return flow from these filters will agitate the surface and prevent that film from forming. (The film itself is a combination of bacteria, salt, food and fish waste and other particles in the water)

You could also try another water conditioner such as AquaSafe which is what I use.

Hope this helps, good luck!


Freshwater Aquarium

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Richard Hight


I own and maintain several freshwater aquariums from 2 to 180 gallon. I can answer most questions about freshwater aquariums, including setup, cycling, maintenance, compatible tank mates, feeding. Moving? I've moved fish both across town and across the country and can help you get your little aquatic friends to their new home safely. I know and have experience with most freshwater community fish, South American Cichlids and African Cichlids. I don't answer questions about Goldfish or keeping Goldfish with Tropical Fish. I also don't answer questions about keeping crustaceans (shrimp, snails, crabs etc) with Tropical Fish, nor questions about saltwater fish or aquariums. I'm not available to answer questions on weekends, this is when I do maintenance on my own tanks.


Many years of personal experience with community tank fish, semi-aggressive fish (Barbs, Tetras, etc), Angels, South American Cichlids and African Cichlids.

HSG 2010-2011 prof

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