Hiya Bloozoo
There are 2 types of Seachem Flourite, one is a mixed colour with the emphasis being on a dark reddish earthy colour, and the other is a plain dark reddish earthy colour (sorry best way i can explain it) so 1 is mixed and the other is all one colour, both are very nice colours IMO, in all respects they look like ordinary gravel that you would put in a tank except a nicer colour.
Here are some pics
Red Flourite (its a bit lighter when washed and in a tank but still darkish earthy red)
red flourite
Normal Flourite
normal flourite
The normal flourite as it would look in a tank
tank pic
So those are the flourites, i dont know how they would be for some of your burrowing fish as they as they are in most respects just like normal gravel.
I dont know much about the Onyx sand, so i double checked on another plant site that i visit to see what other more expert ophinions would be on it (i just read some previous posts in a search)
So here are my findings
It is a dark grey in colour when submerged in water, it will buffer your water, it will raise your Ph because of the carbonate content in it, usually by 0.5.
Most people thought the FE or iron content was better in flourite.
But most who had used it would use an alternative product called Eco Complete if they were to do it again, now these are not my ophinions, just my little bit of market research.
Eco complete is another product you should probably consider, its widely used in the planted world, and its highly thought of, its a very good substrate, its black in colour and would be the nearest to sand you could get as a proper planted substrate.
Heres alink for it
Aquatics Online Eco complete
I couldnt find a pic for it easily, but it looks like a black sand and looks really cool if the background of the tank is also black, it makes the plants and fish really stand out against the black.
Edit: Sugar........i forgot the pics wouldnt show up........but the links still work
