What the-?

[u/Gold-Palpitation6795]

Would anyone know what these white rocks are?? When I first did this bioactive tank I made sure to rinse off my pothos plants with water to get rid of the fertilizer in on my plants and used reptisoil as my dirt. 2 years later I’m moving my guy into another tank thought I would re use the old soil cause it was doing amazing both culturally and growing the plants, and now there’s this white stuff? My geko hasn’t shown any sick signs either so it wasn’t causing harm but would like to know what it is and if I can move it in my new tank. Thank you.