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I have an instant ocean hydrometer and when i measure the water, i find that the specific gravity is high (1.028-1.030) when i measure the water closest to the surface and low (or actually where i want it to be at 1.021-1.024). I've had the tank running with the salt in it for a while (2 weeks) so even mixture isnt a factor. That being said, what is my REAL salinity in my marine tank?

(2 perc clowns, strawberry pseudo, blue damsel, and 3 hermits are doing fine, had them all for a bout a week)

First things first, are your fish and corals behaving normally?
Are they healthy?
If they are ...don't change anything in your routine.

I have an instant ocean hydrometer and when i measure the water, i find that the specific gravity is high (1.028-1.030) when i measure the water closest to the surface and low (or actually where i want it to be at 1.021-1.024). I've had the tank running with the salt in it for a while (2 weeks) so even mixture isnt a factor. That being said, what is my REAL salinity in my marine tank?
We have also had problems with Instant Ocean Hydrometers. I still love their salt, but since they changed styles on their hydrometers
we have seen many inconsistancies. They usually run high, in my opinion. Our current favorite hydrometers are made by Marine Enterprises International, we carry them here at the store.
I have never tried measuring salinity from water at the bottom of a tank, as compared to salinity at the top of a tank (I never even thought about it, we only measure the top water). I find it very difficult to think there might be a difference after TWO WEEKS of mixing...maybe after TWO HOURS of mixing!
Short answer is... I don't know.
But get a more reliable hydrometer.

The only other thing I could think of is that you're getting incredible evaporation at the top of your tank.

the fish seem to be doing fine. they are all eating well including my hermits and snails. how much are those hydrometers you're talkin about?

M.E.I. Hydrometers

We have the lever style for $14.
A floating style for $11...
they also make a labratory grade floating style for about $30...this one we'd have to order.