predators, they do have more intellegance than guppies. Behavioral biologist George Barlow supposedly suggested that they have roughly the untelllegence of wolves. Sometime Google Bartow and cichlids. He had a terrific book come out about 2001. Unfortunately The Cichlid Fishes:
Nature's Grand Experiment in Evolution wasn't widely appreciated until after it had gone out of print. It is available through interlibrary loans and the used book sites. Unfortunately its price is rising rapidly as interest grows and supply declines.
Sounds like a neat tank with the black gravel. Any idea what the "pleco" is and what it eats? :)
If you have mysterious vanishing guppy fry, feed the ghost shrimp more. ;)
I don't exactly know why, stress probably, but ghost shrimp are not supposed to fair as well in glass bottomed aquariums as tanks with some sort of substrate. A little gravel and no reflection seem to accompany longer lives. I guess they feel more secure and for fish, as well as people, that encourages health.
At some shops you can often find ghost shrimp in feeder tanks. But as with other creatures in over crowded, bare-bottomed feeder tanks, ten for a dollar may still not be a good deal.
all the best!