I've got two older male bettas in two separate habitats. For the last two weeks (maybe less) a rather clear film seems to appear at the top of the bowl surfaces. I've changed out the water in portions to doing complete clean outs. I have switched bowl conditioner (the last kind I had wasn't my usual so I wondered if it was doing something, back to my usual now), changed the plants because I thought it might be caused by some glue in the bases. Completely cleaned the gravel with boiled water and a bit of dissolved aquarium salt (then proceeded to rinse the gravel). Scrubbed the bowls even started to feed the bettas less to make sure it's not overfeeding. Took water from different taps pre-conditioning to make sure its not the tap I usually use to rinse / refill.
I always change the water every week, scrub the bowls. The film is a new development. The bowls have never been heated or filtered but its a new problem. Considering all the changes I've made, plants/conditioner/extra cleaning, the film keeps coming back after a few days.
It splits quickly when I drop in food. The fish aren't acting lethargic or unhappy. So I have no idea what the film is. It doesn't look alarming or sickening but I worry it's something trying to grow.
Any ideas would be lovely. Getting filters and heaters isn't really possible for me at this point in time.