Basically I plan to switch my roma 125 over from playsand to a dark substrate. Reason I want a fertilising substrate is to give an extra boost to my swords,valls and crypts. Although I dose the water column, I don't dose EI so this extra bit of compensation would be useful for me. But anyways, problem is I have Bolivian Rams, anyone who has these fish will know they like to filter feed from the bottom of the tank. They take a mouthful of sand and spit it out through their gills, for this reason I really need something small. I've narrowed it down to either Flourite Black Sand, or possibly a mixture of the black sand with tahitian moon sand... So my few questions are... Is flourite black sand smooth enough? If it isn't, could it be mixed with the moon sand without looking silly? Are there any other substrates you can think of that would be suitable for me? Oh and a side note, would you say flourite black sand and tahitian moon sand are heavier or lighter than your average play sand? At the mo my play sand gets 'eroded' in a specific corner of my tank.