Honda specs the lubrication and inspection of the drive chain every 500 m / 800 km. We recommend a graphite-style chain lube along with a solid roller chain that you can find below.
If loose, follow the tightening procedure in the Honda service manual. Chain slack, also called sag, is checked by moving the chain up and down vertically. Specified sag is 10mm - 20mm ( .4 - .8 inches ).
*If you have a later K6 or K7 CB175 and CL175 you will be using a 520 style drive chain.