Need help to bring no3 down

[mahditab1]

My no3 is at 100 or over was told to do a 50% water change did a 103g water change tested it today after a week of running it to my surprise it didn’t even go down what am I doing wrong I need it to get back down to less than 5 my pho is 3 my tank is 220g and my sump is 30g

 

[Randy Holmes-Farley Verified Community Expert]

Duplicate thread.