How many sand sifters to a tank?

[my2rotties]

I was wondering how many sand sifting gobies I should put into my tank. I have about 200 pounds of live sand in the 260g. I have a yellow headed sleeper goby and a dragon goby. Of course they have the two areas in the tank they reside in and do not venture very far from them. I find they keep the sand turned up which helps me out a lot. However, I would like to add a pair of orange spotted gobies to the tank for more sifting.

Is this doable, or a bad idea?