Manage the tank through additions, not subtractions.
Skip the whole lantham-chloride-GFO-carbon-source-dosing-gotta-get-low-nutrients thing. There are innumerable organisms and microorganisms in your reef that are better at consuming dissolved nutrients than you are, but they still may need a little help in our imperfect enfironment.
BTW, feed a healthy amount of the healthiest food you can, all the time.
When you test...
- If you see P rising, but not N – try adding a little N.
- If you see N rising, but not P – try adding a little P.
- If that doesn't work, another factor might be limiting algae/coral growth that should be consuming these basic nutrients.
In that last case, try a water change to restore some level of trace elements to see if that makes even a short-term difference.
Or possibly try an ICP test to look at a range of potential limiting nutrients – unfortunately, iron is one of the "more likely" limiting nutrients and apparently ICP does not test well at the low Fe levels we're interested in.
Dosing some iron is also an option.
And of course, re-check all your basics – flow, lights, etc – makes sure everything is at least normal.
