I have african cichlids (lake malawi type) in my hall pond and they do breed like bunnies. I had 10 to start with and this last week I had to empty the pond for some work and pulled over 50 out. Some have died from the shock but so far I'm keeping most of them alive in big plastic barrels with an air pump. I also bail about 5 gal a day from each barrel and add new water. It's exhausting and I hope I can put the pond back together again soon. My PH is very high, about 8.5, the water from the limestone aquifer here is naturally high and then the pond is concrete which adds to it. I also have large chunks of limestone in the pond as decoration and for the fish to hide. So yeah, it's the PH not the limestone.
I'd love to have Discus in the pond but I'm afraid they won't thrive in that high a PH. I have angels in my outside pond and they are fine, over 4 years old and 6" high. No babies, they lay eggs and try to protect them but the plecos in the pond scarf them up.
