A 120-150 is not a big tank. When you can do a significant water change using a kitchen trash can you are not in the big tank category.
If your utility bill isn't larger than most peoples car payments, or the rent on someones 1 bedroom apartment then you are not in the big tank category.
If you can use teaspoons to measure additives for your tank, then you are not in the big tank category.
If you can take a full tank shot of your tank and see all the fish and corals clearly, then you are not in the big tank category.
If your UPS driver doesn't hate you because of the regular deliveries of heavy cases of salt, then you are not in the big tank category.
If all your equipment and fish tank supplies fit under your tank in the stand, then you are not in the big tank category.
If an entire curling team can't stand in front of your tank to look at it without rubbing shoulders, then you are not in the big tank category.
If you can algae wipe your tank without moving the ladder or step stool, then you are not in the big tank category.
If you take a quick glance at your tank and can see and count all your fish, then you are not in the big tank category.
If you can get two friends to help you move your tank with one trip in the pickup and only a 12 pack, then you are not in the big tank category.
If 9 out of 10 people that walk into your house, don't say "Wow, that's the biggest tank I have ever seen!" then you 'might' not be in the big tank category.
If you have only one door shelf of your freezer dedicated to tank foods, then you are not in the big tank category.
If you don't post about your tang purchases, because you're worried about the tang police, then you are not in the big tank category.
And most importantly, if you have to ask.... Then you definitely don't have a big tank
Dave B