How to add a DSB?

[Canadian Man]

Great advice so far.
You are going through a similar situation to what happened in my 90g tank.

I started off with a 1" layer of more course sand and added sugar type sand in 4 stages up to about 3 to 4 inches.

Just do it in stages, use the pvc trick or I put it in a mesuring cup and brought it down to the bottom and dumped it.
The trick with that is fill the cup with water slowly at the top of the tank and then go to the bottom.

cheers