your tank is beautiful but do you really have slate in there? arent you afraid of it leaching minerals into your water?
Just in case you didn't know.
Chemically slates are multi-mineral rocks made of an aggregate of minerals and colloidal substances. Essentially, mineral composition includes members of mica group commonly sericite & muscovite, clay group commonly paragonite, chlorite & kaonilite. The accessory minerals are oxides, calcites & minor amounts of quartz and feldspar(source of silicates) along with subordinate amounts of ferro-magnesian minerals.