Large Glow in the Dark Fish Tank Cobble Stones ~ Glowing Rocks ~ Aquariums - Gardens These can glow for 8 hours or more when fully charged. Each Bag Contains 8 Large High Polished Stones. Size - approximately 2"x2" These charge the fastest under black, UV or LED light, but will still charge under regular light bulbs Water, acid and alkali resistant - Salt Water tanks are fine Completely safe and non-toxic. Available in Aqua, Blue, and Green