IME placidochromis are not effective at fry control. Mine certainly were not, not fast enough for most small fry. I would get at least 3 syno multi's, they do better in large groups, but 3 would work. A single predatory hap will work, but not if the fry can hide while growing. Small fry are like caviar to a Russian, which is why I suspect that you have to many small nooks and crannies for the fry to hide in. All good if you are wanting fry to survive, not so good if you do not want to have fry in your display tank. My main display tank had large massive granite boulders, lots of caves etc, but too open for fry to last long. It worked well as I did not want fry in that tank.