A 20 gallon tank with 2 powerheads and a power filter? You may have sucked the fry right off the rock! However, there is also the possibility that the eggs were not fertilized, or they could have fungused up. It is not uncommon for a parent to eat the eggs if they feel they are in danger, moving the eggs can cause this. Add one pleco and you have several theories as to what went wrong. I have been most successful at spawning A. compressiceps when the fish have paired up in African community. I let the young pair spawn a couple of times in the community tank to increase their bond. In the community tank I salvage the fry just as they begin to free swim, they will be in a swarm near the front of the shell (they love conk shells) or flower pot. After I have had a few spawns I would then move the pair into a 10 gallon tank by themselves with a couple of shells, after I am sure they have spawned I like to remove the male. I usually get more fry when I let the female raise the brood for a couple of weeks than when I try to do it myself. The fry are very very small, it is amazing that they can even eat brine shrimp. Don't give up, put your three fish back in a community tank and let nature take its course!