I am wondreing if anyone has ever placed a layer of fine gravel or sand on top of their exisitng substrate. I have a 54 gallon which has a combo of flourite and laterlite. I dont want to do a complete tear down, but wish they had made the darker flourite sand at the time I purchased my reg. brown flourite gravel. I really enjoy the look of the darker finer substrates. Can a layer of sand (flourite or any other type that may be better for plants) just be poured directly on top of the exisiting flourite and will it stay? Or would it just end up on the bottom with my laterite? If it does settle through will my substrate then be kind of "clogged up" because all the space between the flourite gravel will be filled in and would this hurt my plants in the long run? Hopefully it can be done and it will stay on top. I hope someone can share their experience if they have tried this.