Unable to groom the tank after 4 years

bro,

I have my marine tank setup in Dec 2004. Since day1, I am not able to keep fishes like Tang, Coral and anemone for more than 3 months. Some die a day or less than a week. My tank is always grown with hairy, brown and red algae. I am very dis-hearten after many years of attempts. I suspect is my setup or maintenance not correct. This year, I started to change partial water regularly, but not very great improvement. Would like to seek for expert advise and help here. Thanks. I just tested my water last night, and this is the parameter.

N02 = 0.2
PH = 7.6
KH = 10

My tank is 3' x 1.8' x 1.8'
Filter = Canister
T5 lighting.


Regards,
Bobie