Depending on the tetra species you can use eco earth coco fiber as a substrate to lower the ph for breeding with a spawning mop or a clump of spagnum moss for the tetras to scatter/lay there eggs on.H Farnsworth said:Looking for some advice from anyone that breeds small tetras. I'm about to set up a 20 gallon breeder with about 20 adults. What should I use for a substrate? or is bare glass fine? Ideal water temps?