14 gallon saltwater tank has high nitrate and nitrite?

i have been having this tank for two months now. i just recently added a small clownfish, a medium sized yellow watchman goby and a blood fire shrimp with snails. my nitrate has always been 20-40 ppm. can't seem to get it down even with a chaeto algae plant. but now my nitrite is 0.2 ppm. i'm a liitle scared with my levels being this way because i have now livestock in my tank and i don't want them to get sick or die. my ph is 8.2 and my ammonia is at 0. how can i lower my nitite and nitrate levels? i've been also doing water changes weekly but that doesn't seem to be helping the problem. what should i do about my levels? do you consider these levels extremely bad?