I advise you to do water changes once a week 25-50% for the first month to have an idea of how much nitrates will be entering your tank on a weekly bases with your bio-load, since your tank is new and you have not had the aquarium for long. Also you should test your water(nitrates, ammonia,nitrite) once a week for the first month or so. This well all help you have a general idea of how many water changes you will need to do and how many weeks you can go without a water change. If after 1 week you accumulate 20 ppm of nitrate in your aquarium that means the next week it we'll be at 40ppm, so I would not go more than 2 weeks without doing a water change.
The highest amount of nitrates you can have in your aquarium is 40ppm anything above can be toxic. Ideally you would want to have 20 or lower ppm of nitrates to be safe. When your nitrates start to reach 20ppm do a water change.
Also if you do not have anything to test your water.
I advise you to buy api liquid master test kit
It contains all the main test for aquariums like Nitrate,Nitrite,Ammonia and ph.
Ammonia,Nitrite in your tank should always be at 0ppm if it is anything above 0 do immediately do a water change, they are both toxic to your fish and can kill them if left unchecked.
You can reduce the amount of time you need to do water changes by adding fast growing plants which naturally absorb the ammonia,nitrite and nitrate in your aquarium Floating plants are really great for this, for the most part any aquarium plants that are fast growing will do a good job.
Some hardy plants you can use are:
Salvinia(floating plant): Very easy to care fast growing, easy to remove, does not need much. Great at soaking up nitrates
Duckweed: Bulletproof hard to kill, Extremely fast growing, does not need anything. The problem with duckweed is that if you decide you do not want them anymore it is extremely hard to remove since it is extremely small, when doing a water change it sticks all over your hand and on everything it touches, It can take over your aquarium and block light, It just need 1 single duckweed to reproduce and take over your aquarium. It is great at soaking nitrates.
Hornwort: Fast growing stem plant, can be floated or planted, little to no care, soaks up lots of nutrients, its pedals can sometimes shed and can cause a mess on your substrate.
water wisteria: Fast growing stem plant that can be floated or planted, easy to care for, It looks quite nice in my opinion, soaks up nitrates
Water sprite: It is the same as water wisteria just has different types of leaves.
You can search online for easy to care for plants there are tons of different selections available these are just a few them.
Plants really help reduce water changes the more you have the more it well help.
For example: Lets say after 1 week your tank will have 20ppm nitrates without plants. When you add floating plants, stem plants, and more fast growing plants it can possibly reduce the amount of nitrates to 10 ppm after a week instead of 20ppm a week. which well mean that instead of having 40 ppm after 2 weeks, you will have 20ppm of nitrates after two weeks instead.
Also they will help absorb the ammonia and nitrites in your aquarium.
