Your stock produces nh3
(from waste) which converts to no3
so even if you didn't add any food or have any fish die no3
still accumulates constantly.
Left over food that your stock doesn't eat is also an nh3
source which converts to no3
. That's why it's critical to only feed what they will consume within one to two minutes.
Your water can be a source of direct no3
as well if it's present in your tap or where ever you get your water from. If you do have no3
is your water supply you can get an RO
filter to remove it.
are important both to remove waste like no3
but also to keep your other parameters balanced.
Also it's important to clean filters weekly so waste that your stock does miss doesn't have a chance to break down and turn into no3