I just added a new power head @6000 lph I already have a 3000lph in there already. But now I'm worrying I have overdone it. It's a 48x24x18
What do you run for water movement?
General guidelines are between 30-50 times DT volume. Your tank is 340L less say 10% for rock and sand = 306L. So 30x306=9,180 and 50*306=15,300
You currently have 6000+3000 = 9000, which is the minimum you want. That's for soft corals. SPS like higher flow.
However, these are old guideline, and people have found the new Jecod/Jebao powerheads and the gyres to be more powerful than traditional powerheads, so you may well get away with less if you have these. If the sand is blowing about, you might have too much (but even then it can be the case with new sand. Once it gets a coating of bacteria, it sticks a bit more, and that can stop).