IMO/E-keeping this species in 1-2gal long term is fine and filters/water movement is optional for this species-especially with the long heavy fin males when kept in smaller containers-often the water movement can be the cause of fin damage.
Are the plants live plants, if so, how many and what species-active growing live plants IMO/E are great filters to help maintain water quality.
What is your water temp
It sounds like you are providing good care, however, if you don't have live plants-adding a second 50% water only change could benefit.
Also, even with bottled water-I would recommend that you use a good dechlorinator and even cut the water with 25-50% of your tap water to replace any lost minerals-Bottled water can vary since its not regulated-it may be filtered tap water that still contains chlorine/chloramine as well as the filtering process that remove the minerals needed for long term health.
Nutrition-good quality varied diet fed in small frequent meals is best.
Love to see some pics.....