Tank cleaning?

[MikeP]

I'm fixing up an old tank. The person that had it before (my dad) had siliconed pieces of slate rock to the back. There are still marks from the silicone and I was wondering what I can use to try and get them off. A lot of the marks can be seen but not 'felt'. Also the tank just generally needs all of the glass cleaned up. what should I use?

Thanks