That's good news: zero ammonia and readings of
nitrite and nitrates. That means you already have in your tank enough beneficial bacteria to brake down ammonia. I suggest you figure out the species of life you have. I noticed the anemona you have there (looks like haitian species to me but I'm no expert) so you rule out any possible pest gaining ground in your tank (if they conquer your tank it will be harder to erradicate/control).
I love your long marine tank. Have you considered upgrading the sand substrate so you end up with a deep sand bed? I believe at least 4" will do the work.
One comment on your set-up. Consider removing the
canister filter. The use of these type of filters in marine set-up requires an insanely frequent maintenance routine or you end up with a genuine
nitrate factory. Low nitrate levels are more critical than with
FW.
Pepetj
Santo Domingo