Tank setup done wrong, can I reuse the substrate
My brother was setting up his first aquarium, he got one of those 54L tetra starter kits and some tropica plant growth aquarium health soil substate but put the entire 9L in and its covering half the tank but he has filled it with water, added seiryu rocks and planted some plants already. The filter isn't fully submerged either and he decided to give it a go without asking me or watching videos.
Is it okay if I drain the tank (was setup 12 hours ago), carefully pull the plants out and rock and take half the substrate out, add the rock back and the plants once filter is seated properly or does this specific substrate cause an issue if I remove half of it as its somewhat settled and should get some more?
Thanks in advance!