Check my 6 gallon containers last night and they are #5's. Did some research and for what it is worth, this is what I found regarding what the recycling numbers mean. It sounds to me that they most all CAN be food grade but not all are:
http://virtualweberbullet.com/plastics.html
I then figured I would email the mfg. of the containers I have. I like the 6 gallon size as they are easy to move around when full. These are what I am using:
http://www.sterilite.com/ProductDetail.html?ProductId=388&Section=Household
And this is the email I got back from the mfg.:
Thank you for your interest in Sterilite products. Thank you for your
inquiry concerning our product make-up. Sterilite
Corporation manufactures our storage products from a material known as
polypropylene. This material is FDA approved and is the same material
used to produce all of our food storage items. Our polypropylene
products do not give off toxicants. No PVC's, Latex, Teflon, or
antibacterial chemicals are used in our manufacturing process.
They are safe to house pets, including fish. As with any container you
plan to use for housing fish, or for aquarium water, you will want to
thoroughly clean the container with a safe fish tank cleanser and rinse
well before use.
Thank you,
Sue Patton
Consumer Support
Customer Service Dept.
Sterilite Corporation
So I think I am safe with these. Am I missing something?