how do you add sand to make a DSB

the back ground:
getting ready to exchange a 29 for a 55 sump/fuge! my DT is a 75 with 2.25" sand bed. it use to have more when i set it up a little over a year ago, approx 4" but then i got the 29 and set up a fuge/sump with it and to house some of the bullied fish. using some of thew sand from the 75, hench im down to the 2.25 of fine sand bed. i remember befor i set up the sump that the bed had started to form the gas /air pockets which is the nitrates turning into nitrogen. but havent see it with the current depth of bed, so to my question.

how do i add new sand/ aragonite to the 75? i have deteris on top and i know i cant get it all off, thinking if i just cover it it would cause a ammonia spike. the other optin is gonna do the same i think if i was to mix the new in with the old. how would you proceed? a side note i will be reusing the sand from the 29 for the 55 and adding more to that as well so thats gonna be distirbed anyway. im thinking of just mixing it and starting the bed off per say new again (killing what bugs are in there) in both tanks and be on gaurd for a spike and just do some water changes.

 

A large piece of pvc and a funnel will keep you from causing a sandstorm

 

+1 on that

 

Don't cover big areas at once. Instead do like a double fist sized area per week to allow the microfauna time to inhabit the new sand.