The DOC's should level off in a marine tank. They do in natural marine environments, such as Mangrove forest, just like they do in FW swamps.

They are not quite sure why, but bacteria likely get going and take care of it.

The smaller daily WC's works well.
Alan did this several years ago with excellent results for some trade offs he wanted(way way way way too high a fish load to mitigate algae and still keep plants).

Basically what I am saying is that WC's or test kits can be used or as most suggest on most forums, a combination of both. I used to suggest test kits and water changes about a decade or so ago.

Most did.

I gave it some thought and a reality check on how folks actually test, why we really need test kits, then applied it to EI. However, you can do the same using test kits and not doing water changes, with good CO2, the results are quite good as well.

Thing is, name one person who really likes using test kits week after week after week..........can you automate testing/test kits?

Not for NH4, NO3, PO4, K+, Ca, Mg.

So.........

Can you automate water changes?
You bet.

So go with which method you can reduce the work load.

I really think given responses I've heard from the anti water change PPS crowd that they never thought this through very well.
Most would like to avoid a WC, same with test kits, but only one CO2 method allows you to avoid both:idea:

Also, if you plumb the solenoids correctly, you can back wash the canister filters when you do a water change(turn a couple of balls valves from the drain to direct the wastewater through the canister backwashing it clean)

Now:
No testing/test kits
No manual labor water changes
No filter cleaning (or greatly reduced)
More consistent flow rates(filter is cleaned often, less organic matter, higher O2 levels)
Much better export.

More time to spend gardening etc.
The concentration ratios suggested are also basically EI light which, well, is not hard to add less and dosed daily.

The same can be done by reducing the rate of growth with the non CO2 planted tank approach. No need for water changes, testing(you can if you want, never seen a need as far as care goes), and greatly reduced gardening requirements.

I'd suggest doing a small non CO2 tank as well.

Regards,
Tom Barr