I’ll chime in with zero hydro experience here. 
Perlite breaks down into dust easily, clogging shit. But it’s cheap, light, & washes out easier than LECA(“hydroton”, clay balls).
Clay pebbles will last forever(ish) but are allegedly a nighmare to thoroughly rinse out, perhaps certain salts/nutes cling to it more than others, leading to a buildup over time. Like your shower. 
