After about 8-12 hours hovering in the bottom corner they have all gone up and been swimming around normally for about 8 hours now. Go figure.

I found a another forum where someone suggested they may be laying eggs. Where is it described how black moors lay eggs?

They are NOT laying eggs.

It may be ammonia levels. A dipstick test for ammonia shows it is in the "stress" level. But this creates more questions than it answers. Three aquariums handled the same. Why does one have elevated ammonia? Three black moors in each tank. Why does the large one show symptoms and the two smaller ones not show symptoms?

They could be stressed or have a swim bladder problem. I used to have black moores and they would act like that when they were stressed. I also lost a few to swim bladder problems and they would float upside down at the bottom and look dead and then get up and swim normally up the right way again...then a week or so later they would die :( Hope thats not whats happening with yours.