I'm not convinced there is a perfect depth to a DSB, but I agree with grain size and using aragonite sand.
I am also a proponent of plenums, but it would really be hard for you to insert one.
I use a plenum in the sump with .05-.07 mm sand to a depth of 4 inches or so, and a shallow sand bed in the tank (approx 3/4 to 1-1/4 inches)
In a system that I ran like this for three years, I never had any detectable nitrate, and pH was always in the ballpark.
I light my refugiums 24/7 and that certainly helps things out.
I'd go with the siphoning idea. Vitz makes a good point on removing bads quickly, and adding good water to replace. The disturbance should be minimal, but it wouldn't hurt to add dusting of live sand to the top layer once you add the SSB in. A 2 inch diameter piece of PVC pipe is usefull for pouring in the new sand, and keeps the cloudiness factor to a minimum. Make sure you turn off all pumps when you add the sand.
To be on the safe side, watch ammonia for a few days after the change
I am also a proponent of plenums, but it would really be hard for you to insert one.
I use a plenum in the sump with .05-.07 mm sand to a depth of 4 inches or so, and a shallow sand bed in the tank (approx 3/4 to 1-1/4 inches)
In a system that I ran like this for three years, I never had any detectable nitrate, and pH was always in the ballpark.
I light my refugiums 24/7 and that certainly helps things out.
I'd go with the siphoning idea. Vitz makes a good point on removing bads quickly, and adding good water to replace. The disturbance should be minimal, but it wouldn't hurt to add dusting of live sand to the top layer once you add the SSB in. A 2 inch diameter piece of PVC pipe is usefull for pouring in the new sand, and keeps the cloudiness factor to a minimum. Make sure you turn off all pumps when you add the sand.
To be on the safe side, watch ammonia for a few days after the change
