Well, I haven't had a chance to take my new boat out yet but I do have some waterspots on my Lowrance 520C screen and wanted to know what you guys clean your screens with.

Is it ok to use Windex? I've heard never to use it so I was curious, I don't want to mess up this $650 unit. If Windex is bad, what do you guys use?

Ammonia is the thing to avoid like the plague.

I use a 50/50 mixture of isoprophyl alcohol and distilled water like Lowrance recommends.  Spray it on and use the cloth that came with the unit.  After a few times throw the cloth in the washing machine.  I don't use any fabric softner in that load as it inhibits water pickup by the cloth.

I use cleaning wipes for lcd computer monitor screens works great.