i have decided i want black substrate and really keen on buying the Pisces Natural Quartz Gravel Diamond Black and then i noticed that the pieces are really really small but they seem light this got me wondering if i can use a gravel vac on them or will they all just get sucked in. i will be keeping an arowana and a few other fish in there and it will get quite messy so i would want to be able to gravel vac it. so would i be better with the Pisces Natural Quartz Gravel Diamond Black which i think looks really nice or just normal black gravel?