This stuff is just fine to use. Even nylon tubing is fine if it is potable water rated, which you won't likely find. Nylon actually absorbs water and degrades over time so it is really suitable only as a siphon tube or in dry air systems where moisture contact is minimal.
For aquarium use there are three types of readily available, inexpensive tubing that are best to use:
(listed in order of durability)
PVC
Blended PVC / Polyurethane (This is what is most commonly sold as aquarium tubing)
PET
Silicone and high purity silicone are ideal, but expensive and sometimes hard to find for the hobbyist.
I should note that one must be very, very careful in choosing tubing for use with water. Many FDA approved for food use tubings have anti-bacterial and anti-fungal treatments which may be harmful to amphibians. Most often it is a result of the use of pure silver mixed in with the polymer, but sometimes copper and or unpronounceable chemicals you never heard of are used. Avoid these at all costs.
As an industrial maintenance technician specializing in robotics and automation, I work with tubing for pneumatic and hydraulic systems pretty much daily. I too save the scraps and bring them home for use with my various projects, when the tubing is suitable.I include links to both McMaster-Carr and MSC industrial supply here as they have quite a bit of useful information on tubing. I do not recommend purchasing from them as they are expensive. You can get the same stuff for much less money elsewhere.
McMaster-Carr
Browse the MSC Big Book