I have two male bettas in a divided 2.5 gallon tank with a clip on led light and a heater, no filter. I've been doing 50% water changes every other day and 100% every week. I've been noticing a thin film on the top of the water it almost looks like a type of oil. I've been adding prime when I get water out of faucet and one capful of betta basics as a conditioner when I change water. The film is still there even a few hours after a water change. I'm taking the water to be tested this afternoon, but any clues as to what this oil film may be?
I also have a couple questions about the water changes. When you do 50% do you vacuum the gravel or change water only? And with a 100% I've been removing all decorations and rinsing them and gravel. Is that good or too much?
I know bettas like a floating plant. Could I add duckweed or is my light not strong enough? Thanks