Can You Solve this Ice Diamond Riddle? ft. Vsauce’s Michael Stevens

Water level has to go down. The reason that an icecube without any extra diamond doesnt change the level is because as it melts it becomes water and replaces the exact amount it submerges when in ice form but with the added weight of the diamond it sinks in more and as it melts and the diamond doesnt it cant replace all the water by itself thus the level lowers.