Recommended or a reef---level of 2 or less.
For a FOWLR tank or fish-only: less than 30.
For many inverts, the survival limit: under 40.
Fish survival limit---maybe 100, but it's not going to be happy.

Some things actually use up nitrate: clams, for instance, reduce nitrate, but have many other high-end life requirements, so don't dump some poor clam into a fish-only.
Some corals like elegance also appear to require a little, so zero is not good for them....

A corals-first marine tank...
I've discussed this a couple of places, and some people are doing it, but let me put forward the advantages and the problems---if you have done or are contemplating doing it, chime in. It's at least worth a consideration, counting how prevalent parasites seem to have gotten in the hobby...

Pros
You can start setting up right after cycle.
You put your cuc in, dip, (do a short observation after dip for zoas, particularly) put a number...

How secure do you WANT your rockwork?
My answer is 'not secure'. I balance, prop, lay it a bit like decorative brickwork, but what the ancients called 'drystane' or dry-stone, despite it being underwater. This means I rely on natural balance, I make my arches out of post-and-lintel and rely on gravity, and I do everything I can that way.

Why? Why not make it one rigid form that nothing can ever shake?

Because I have had to go in and do a fish-extraction that...

Do you need fish at all?
Short answer, no, not really.
Many people assume corals are the hard stuff. Some are. Many are so easy you have to be careful or they'll be like crabgrass.

One of the problems people have as NTTH folk (new) is assuming fish are tough. Most marine fish aren't that tough. Not all corals are. But some corals are kill-them-with-flamethrowers tough.

Corals do emit waste, but moderately so. They'll live on light (literally: their colors...

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