deep sand bad and joubert

Hi

I'm starting a new marine tank and i would like to try without other
filtration than sand bad, and some pumps, some live rocks

i would like to keep 3 max 4 small fish and maybe some actinodiscus or
discosoma or something like that

i was thinking to make 50% of sand bed with joubert method and 50 DSB 10 cm
high

my tank is 120L, sorry buth i'm italain :-)

i sow live sand in a shop it is coral sand with some water in a plastick
seald bag, it has an expiration date... it is 1st time i see it, do you
know if is good?

whath you think about my tank project and how long do you think it will
take to be fine for fish?