Nitrate Problem
 

Im sure this is a very common problem, but my tank has been established for almost 2 years..
is 120 G, have skimmer, cheato, couple mangroves... dosing Zeo start2
been doing water changes more frequent.. yet the levels are still high..
my bubble coral's health is declining because of it
any suggestions ?

Make sure you harvest a lot of chaeto. It has to be growing to be sucking out nitrate.

How much do i need ??

how much are you feeding the fish and what are you feeding them? uneaten food can contribute to nitrate issues.

I am feeding just mysis shrimp
i do it once every 2-3 days...

How deep is your sandbed? Are your mangroves actively growing and putting on new leaves (while retaining the older leaves)? Same with the Chaeto, if it's not actively growing it's not consuming nutrients. How often do you do water changes?

git rid of all he filter media you have and things should be fine. There is no way you only feed once every 3 days, grow chateo, and have a skimmer and still have nitrate problems. Check your water source and maybe your test kits.

Make sure to rinse out your Mysis before feeding too.