Tetras aren't pure carnivores, they are also omnivores, so eating plant material is common. It's perfectly OK for them to eat algae wafers if they like them. Also spirulina is good for them as well which is found in a lot of the tropical wafers. It helps to keep them regular as a lot of their food also has a lot of fat which can cause problems if it is the only source of food they get. But the algae wafer shouldn't be their only source of food. They need it from time to time, but you might have to be a bit strategic in order to get them the food they need and the algae wafer to the bottom of the tank for your other fish. You can distract them with flakes at the top of one side of your tank, and while they are busy eating that, you drop the wafer on the opposite side of the tank so it reaches the bottom before they even know it went in. In any event, I found
this article at Dr. Foster & Smith's site while checking out the different food for my fish, then I also found
this Q&A which gives some good tips to help your fish eat healthy.