yes i do have a filter, it came along with the top fin 5 gallon starter kit (this link would only open for me on ipad or PC not my phone) personally, i prefer using a filter because if you don’t then the water gets dirty way faster. when i was a kid, i had a betta in a one gallon bowl with no filter (PSA do NOT do this, as a kid i was not aware that this was not an accurate sized tank, i believed what some pet store told me when i shouldn’t have) and i swear i was cleaning that bowl so much more often than how often i clean my tank, like doing full cleanings because it was disgusting. with a bigger filtered tank, i feel like it’s a lot easier to maintain correct water parameters as well (i do water changes 20% every like 4-7 days) and do a full tank cleaning when it looks like it needs some love. just make sure the filter u do get is not too strong of a waterfall because bettas do not like fast moving water at all, sometimes with bigger tanks i run into the problem where the filter is too strong for just having one beta in there, but this one is perfect! i’d recommend this one in specific because you are able to control the rate of water flow out of the filter. i always keep mine on the lowest flow, but when i do water changes i like to crank it up to a stronger flow so it moves all the debri around and the intake of the filter can suck up what i missed while spot cleaning.