What I recommend on 1.5gal filtered tanks-twice weekly 50%....1-50% water only and 1-50% to include the substrate by vacuum or stir and dip method. Leaving him in the tank for water changes.
Filter media needs a swish/rinse in the bucket of old tank water a couple of times a month.
While the smaller filtered tanks can establish the nitrogen cycle-often it will not be stable due to the limited surface area and why I recommend twice weekly water changes regardless of cycling stage/completeness on tanks under 5gal.
I do recommend master freshwater test kit to monitor water prams, however, you don't have to have one on hand to successfully keep a Betta-especially since you can have your water tested for free at the pet shop-Plus-regardless of the test results you will most likely do the same thing....Water change.....
IMO/E-the 1-2gal tank is fine to keep a Long fin male long term- provided that you make the needed water changes, maintain temp (76-80F
) and don't overfeed.
I have found that Long fin males will sometimes have problems in smaller tanks with a filter-sometimes the water movement can be the cause of fin damage and stress on Long fin males.
IMO/E-filters are optional with this species-especially in smaller tanks.
Without a filter water changes would still be twice weekly...1-50% water only and 1-100% to maintain water quality.
*Note-when making 100% water changes and you remove the Betta to a holding container-It is important to re-acclimate to the new dechlorinated water by adding small amount of new tank water to the holding container over 15 min or to tolerance-net and add back to the tank-Top off tank as needed with dechlorinated water.
IME-I have found that Betta don't produce the amount of byproducts that you might think-most water quality issues stem from overfeeding and/or poor quality foods.
Nutrition-good quality varied diet fed in small frequent meals.