I have two 2.5 minibows. That are filtered. I have been changing the water every week. But I noticed my two bettas had some fin damage ( Sunti bit his tail and Suchin split her dorsal fin somehow) I noticed since the last water change ( it has almost been two weeks) that their fins are healing quicker than when I change the water once a week. Maybe once a week is stresssing them out too much. I am also planning on upping Suchin's tank to a 5 gallon minibow. With the 5 gallon should I only have to change about .25 of the Water?

I have a 2.5 minibow and I remove 50% water once a week. My 2.5 gallon houses a tiny male mustard gas crowntail and a brig. I keep plants in it and use ferts and co2 a lot so its important that I change the water at least once a week. Do a test and see how long you can go before you parameters start to change.

BTW- Halfmoons are notorious self fin nippers.

Thanks Sushi. Yup I have discovered that about him. He is still doing it. I keep indian almond leaf in there all the time and salt the tank too. I think I may have to add some bettafix too.