I'm no expert, but have been playing with DHG for a few years, and:
1) Removing the potting soil was probably a good idea, as it'll make your water parameters pretty wild once you try filling the tank with water (ammonia-spikes), and you'll have a partial amount that will float. Some ppl put potting soil under a layer of inert substrate like sand. I read boiling helps with the floating issue; read through Tom Barr's site for more on this. But, I don't see why smell should be a factor once it's under water.
2) Spreading your hairgrass into as few blades (maybe three) per planting is key. Think of it this way: each chain of grass will only send out runners in two directions-- from it's ends. The more clumps, the more ends.