When I was gathering various tubs and containers to use in my aquarium maintenance, I wondered what plastic containers would be suitable and safe to use. I didn’t want a plastic container that would leach harmful chemicals into the water I was transferring.
The answer turned out to be simple, and relates to those little recycle symbols that are on the bottom of plastic containers.
Decoding the Recycle Symbol for Aquarium Safe Plastics:
A plastic that is aquarium safe will also be food safe. Which is to say, the best containers to safely store foods are the best to use for your aquarium maintenance needs.
The little recycle symbol (three arrows formed into a triangle with a number in the center) helps recycle centers to identify resin plastics of like kind. The best type of plastic for use with foods have the number 2 in the center. These are plastics made of high-density polyethylene (HDPE). Compared to other types of plastics that are categorized (numbers 1 through 7), HDPE is relatively stable and inert. This means that it doesn’t leach chemicals into food or fluids over time. This makes HDPE plastics with the #2 recycle symbol aquarium safe. From what I see, #2 plastics tend to be used for items that have a bit more strength and stiffness.
A close second to #2 plastics are #4 and #5 plastics. #4 plastics are Low Density Polyethylene, or LDPE. #5 plastics are Polypropylene. Polypropylene plastics have a high tolerance to heat, so many microwavable containers are made of polypropylene.
The only food grade plastic that I would avoid for aquarium use are #1 plastics. These are PETE or PET plastics, and are often used for one time usage items like plastic water bottles. These plastics are a little more unstable and can leach chemicals more readily if used over time.
I’d have a preference for seeing the #2 or #5 symbols for items that I was using for an aquarium. My large Home Depot bucket is a #2 plastic. The remainder of my small rubbermaid or tupperware containers that I use with the aquarium are #5 Polypropylene.