There is a bit of misinformation in this thread. Bettas are like every other fish. They need clean water. Weekly water changes are a necessity to remove total dissolved solids and nitrate. The new water dilutes the nitrate and TDS
and introduces vital minerals/buffers needed for stable water conditions, fish and plant health. The OPs tank is cycling she NEEDS to do daily water changes to dilute the ammonia and nitrite being built up in the small tank. Without this the Betta will be getting ammonia/nutrite burns to his gills.