Hydrometer vs Refractometer

[Hairytank]

Yesterday I bought a Sybon Refractometer at Red Coral and today... I am horrified!
I have been using a Coalife Deep Six Hydrometer and my readings have been between 1.025 to 1.026 and have been so for about 4 months with very little change ever since I bought a Tunae ATO.
I messured the Specific Gravity with the new Sybon, my water tested out at 1.029! I tested the purified water sample that came with it to ensure it was calibrated correctly at the factory (it was).

Having the SG at this level is not fatal (obviously), but is probably partially responsible for the slower growth of some of the corals. I will lower the SG levels to 1.026 over the period of a week or more.

I find it amazing that there can be a .004 difference between these two instruments.

I would be interested in anyone with similar experiences.