S$250 is daylight robbery, just get the chemical yourself and you can it yourself, no need depend on these contractors
 
	You can get the chemical called HCL89.
 
	I usually get it from http://hcl89.byethost10.com or http://hcl89.atwebpages.com
 
	What it does is that it cleans your wall tiles/glass and also helps to create a protection for it so that always remains new.
 
	Hope this helps you out