I copy this post from other site..hope it help a little...Right now I have 2-3 colony get STN so I will try to do this..I had been change 5% water every 2 days since last week till now also lower the ALK to 7..It's help a little but not much..
Here we go:
1. Superglue well above the Necrosis area - This works well for localized events and when there is STN. In cases that are tankwide events this method may not be feasible. In addition, in the cases of RTN, gluesuper only works if you catch it in the very early stages.
2. Reduce Lighting Intensity - This needs to be considered in the tool-kit to battle Necrosis. If corals are getting too much light, they cannot repair their tissue. This weakness could cause RTN or STN.
3. Increase Feedings or Nutrients - I believe it is far more likely that corals in starved aquariums are more likely to experience Necrosis. Acropora in higher nutrients typically just brown out. Increase feeding if your corals in general are pale and experiencing Necrosis.
4. Double Check Parameters, in Particular, Alkalinity - Low Alkalinity it probably the number 1 cause of Necrosis. Find the nicest and most successful aquarium in your area and grab a water sample and match their parameters with your test kits.
5. Ensure you don't have leaking voltage - Leaking voltage may be the cause of RTN and STN but this is highly debatable. Obviously removing voltage from the aquarium solving a safety concern, so you can't exactly argue against this solution, even if there is no link.
6. Inspect for Coral Eating Critters - I believe that astrenia starfish were rubbing on the edges/bases of my SPS causing STN. Remove these animals from your aquarium if you're experiencing Necrosis.
7. Nail your Salinity down - Again, find a tank in your area that has had long term success and match their salinity with your instruments.
