Luananeko
Aquarium Advice Addict
+1 to the Purigen being the cause of zero nitrates. That stuff works amazingly well so long as you keep it recharged at appropriate intervals.
Regardless of the nitrate levels, it's not a bad idea to do larger water changes than what you're doing. Doing so helps replace vitamins and trace minerals that keep your fish immunities high. Since you don't have plants this isn't as critical as it would be in a planted tank (plants deplete the nutrients on top of what the fish are consuming), but it's still a good habit to be in. If you're doing water changes with a python or auto-water changer instead of the bucket brigade, and have good tap water, it makes larger water changes a snap.
Either way, it sounds like what you're doing is working. Keep it up
Regardless of the nitrate levels, it's not a bad idea to do larger water changes than what you're doing. Doing so helps replace vitamins and trace minerals that keep your fish immunities high. Since you don't have plants this isn't as critical as it would be in a planted tank (plants deplete the nutrients on top of what the fish are consuming), but it's still a good habit to be in. If you're doing water changes with a python or auto-water changer instead of the bucket brigade, and have good tap water, it makes larger water changes a snap.
Either way, it sounds like what you're doing is working. Keep it up
