not a expert but having similar issue. 29g ..water in check except my nitrates between 20 and 40 with my api test kit. I was always told it reads high especially the nitrate kit , everything alive in my tank seems happy besides my blenny who is stil getting used to having a pair of clowns with him now.
ive been keeping up on water changes from day 1 and really have a problem getting nitrate lower ...if you consider it a problem which i consider it more of a personal goal now since everyone in the tank seems happy and doing great.
my 29g isnt a biocube so my new project is filtration and such...running a HOB
which I clean weekly and honestly dont think its the reason for higher nitrates like most things ive read , I also use distilled water for everything. I think its more of a case of newbie overfeeding and think I need some macro algae like you have had mentioned to you also
I have also been using microbe lift special blend to help boost my bio-filter and keeping water clean , it mentions helping with nitrates also ... haven't been using long enough to see if it will help that much.... I am in process of getting more rock for decoration and with seeding will help more with my bio-filter and getting some macro algae but i want some I can use to decorate with since Im FOWLR
and have no corals ... will help with the eye candy of the tank also