I have heard it takes having one more cave than you have males. Feeding live or frozen food to them is also supposed to induce breeding. Fresh zucchini and sometimes asparagus is used. And a lot of patience. some say the tanins are needed and some say that the pH is the key. Many pleco are bred without the tanins as it seems that correct conditions are mor eimportant. I have also heard that if the pleco feel there is any predator in the tank that will eat the eggs they will not spawn.