I agree with Spoonman, Foam underneath glass tanks is not recommended because it creates pressure points on the bottom of the glass where the base and stand mate causing the glass to crack (that's if the stand has a solid surface for the tank to rest on). Glass tanks are designed to be support by the edges, My 120 stand only supports the tank around the edges and center brace. Foam is suppose to be used when an Acrylic tank is being employed and even so it's usually only about 1/8 to 1/4 inch thick, this is because the acrylic tank needs to be completely supported on the bottom.
As far as the Hydrometer is concerned i find them to be pretty much useless. I had my water checked by 4 LFS
's for SG
and all of the readings were different and not one matched my IO Hydrometer, mind you this was done the same day with the same water. I bought a refractometer and am now confident of MY SG
ditch the HYDRO and get a refractometer, It's too important to be screwing around with a notoriously inaccurate device. I'm not willing to trust a 6 or 7 dollar device when it comes to the well being of my fish. OK I feel better now.
If you have the time, take a container of DT water to several Shops and have them measure your SG
and see what they come up with. The variations I had was from 1.016 to 1.024 with mine reading 1.026, If the window was closer I would still be using the HYDRO, but since it was so great I got confused and angry with the device. I even contacted IO regarding the problem and they just re-iterated the instructions I was already following. I'm going to try what your LFS
had you do just to test it out, however this wont have me using it again because they are NG and I don't want that thing floating around my tank all of the time because I check it every day.