Last week I did add a Fighting Conch and a few Nassarius snails.
I haven't measured any Phosphates or Nitrates in the water. I was stirring up the sand bed during bi-monthly water changes, but I stopped a few months ago. I think my tank was to clean, my Duncan coral which was doing very well had started to recede.
I had done a 25 gallon water change after stirring up part of the sand bed and blowing off my rock in the DT. The water got a bit cloudy, I added one cup of carbon, thats when the Duncan coral started looking poor. Since then I haven't stirred up the sand bed or blown off the rock. I also took out the sock I was using in my sump, I had been changing it every 3 days.
Now the Duncan coral is looking better. I think I'll go back to stirring up a 1/4 of the DT sand bed when I do water changes and try that.