I have 2 female bettas in a divided 5 gallon tank - no heater as I got them over the summer and it's been so warm so far, and no filter. I tried a filter but the current was just way too strong for the poor things and they got blown to the other side and struggled constantly when it was running.
I feed them BettaMin Tropical Medley flakes, they seem to love it. I do 25% water changes every other day and 50% on Mondays (office tank- they are alone Saturday and Sunday). I go a gravel clean at least once a month. I age the water between changes
They have been very happy in their new home for weeks - deep, vibrant colors, playing and diving, rushing to the glass when anyone comes near it looking excited because they think they'll be fed, etc. They have normal interaction with each other through the mesh divider, a fair amount of hiding and a fair amount of "chasing" the other.
I was out sick a chunk of this week and a coworker was feeding them. They hadn't had a water change in a few days because of it so I did that right away.
One of them is extremely pale. Almost no color at all, and she is usually dark, dark red - almost tiger striped at times. I know they get pale from stress, but I can't figure out what would be stressing her out.
The other fish is still very dark and vibrant, actually almost more so than usual. She does, however, look a little fat. I don't know a lot about fish gestation periods, but I've had her for 3 months and she hasn't seen a male betta the whole time. I don't think she's pregnant.
It's very possible that they were overfed the last few days I was out. But would that cause one of them to get so pale?
I don't have water parameters as I don't have a test kit in my office, however since only 1 of them seems to be so stressed I feel like it's not water conditions making her that way. Neither of them have any spots or any of the usual disease signs.