How long do you keep your lights on?
The food you are feeding is not very good....Flakes at best are only good for a snack maybe 1x a week, and brine has the nutrition of a potato chip.....Some good foods are frozen mysis, marine cuisine, emerald entree.... and for 1 fish, you only need a small piece of the cube.
How often do you do water changes? You should NOT be dosing anything unless you test for it. In fact, If you do regular water changes you should not have to does anything at all
part of your problem may be too much nutrients....another part is your clean up crew
I would go get some nassarius snails and some cerith snails...maybe 6 of each for now, and why do you think a shrimp would help you out???
As far as your level of trites and trates...what do you consider good? Can you give the exact test readings of everything?