I don't think they are inert. It's like saying plastic bottles are inert, but we keep hearing about certain types of plastic slowly releasing PCBs or BPAs.
The only inert things we can safely say are gold, diamond, platinum....
I vote for fluorite slowly releasing nutrients and not completely locked up. Especially with time, bacteria and constant water contact.
Given that, the releasing rate is probably too slow therefore you would need to fertilize in the water column and have root tabs.
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15G Planted Aquarium of Red Cherry Shrimps, Crystal Red, Black Shrimps & cute dwarf puffer. :p
50G Planted Aquarium of 6 Goldfishes, 2 Weather Loaches, 4 Silver Cories & 1 Pleco.
20G Planted Aquarium - Emerald Green , Tiger & Blue Pearl shrimp tank.
10G Office/Lab Planted Aquarium with Neons and Galaxy Rasboras
5G Hexagon Aquarium of baby Goldfishes.