Adding sand to existing fuge?

I have about an inch and a half of sand in my fuge right now, its been up for about four months now, would adding new sand to this existing bed be okay for my tank?

 

IME
yes , you could add some more sand , your existing sand bed is only very young at 4 months old so does not present the same type of problems as you might have with an older, deeper sand bed

I would add in stages
take a cup of existing sand out
spread a new layer of about 1/4 inch on top of existing bed and then replace the cup of sand you took out over the top of that
repeat this every couple of weeks until you have the sand bed depth you require

Steve