Hello and welcome to 3reef first of all!
As for the live sand? I'm sure you have some die off which is the reason why it smells. I would try removing some of that by rinsing it under some salt water and possibly place a filter and powerhead in the bucket as well to help aerate and also remove as much die off as possible. The other thing you can do is rinse quickly and just put it in your new 125. The cycle is inevitable and this will help to start your cycle in the new tank. This is just my opinion however!
good luck with the new tank! And again welcome aboard! _________ 125gal.w/Mag9.5 return(dual megaflow)>Mag7 pump Aqua Cev180skimmer.Wave2k Hamilton Reefstar(2)250watthqi(mh)pend.a Yellow, Naso Tang Red Lip Blenny Percula Clown Demoiselles Niger Trigger F. Wrasses Ceriantharia Orn.Shrimp and Stars Hermits Queen Conch asst. snails> Stars Zoos shrooms Montipora Brains Gorgonians Favia Turbinaria(large+small polyp) Acropora Xenia Tridacna (CroceaMaximaSquamosa) Leathers <35+75gal.reef tank as well> 
"IF THE PHONE DOESN'T RING...IT'S ME"  jb  |