STN from hell, please help

[DanTheReefer]

Remember that corals have a delayed response to stress. You mentioned many things that happened in addition to the initial crash of nitrates.

Large water changes – drastically shifts tank parameters and depletes DOC and nutrients
Use of ROX – Aggressive use can strip DOC and trace elements
Changes in alkalinity
Sudden changes in Phosphate from 0.350 to something lower
Sudden changes in Nitrate from 0 to 10ppm
Dosing antibiotics

Each change individually is capable of inducing STN / RTN.

In my opinion, the most important thing to do is to stabilize the parameters, and wait it out. Unfortunately the situation is likely to get worse before it gets better.

When I have an issue with SPS, I like to reset my parameters to my normal parameter setpoints, and go into what I call “Save Mode” with the following checklist:

4 to 5 20% water changes over a few days
Alk to 7.5
Nitrate to 5 ppm
Phosphate to 0.050 ppm
No GAC
No GFO
No UV
Reduce lighting to <300 PAR
Verify good 100x flow
Verify salt SG to 34-35 ppt
Verify temperature 79.5
ICP test
Verify no pests
Dose Acropower if corals appear to be starved
Dose vinegar 18 mL/100 gal if corals appear to be starved
If RTN, then frag off healthy tissue
Test, test, test, and keep everything rock stable
Continue moderate water changes as necessary

Your setpoints will likely be different, but you get the idea.

This video explains some thoughts about the complexity of bacterial infections in corals.

Thank you for sharing, fascinating

 

[jeffyang]

I think you will be better off without adding anything to your tank at this point. Just keep the basic parameters stable and wait out.