I finally went and bout a testing kit and tested my water my GH Is 11 (195ppm) and my KH is 5 (125ppm). I also keep African cichlids and they seem to be doing well although I now know my alkalinity is very low for them. That is the tank I tested also could calceous rocks and crushed coral affect my readings?
Hi, I would be more concerned about the african cichlids than the plants. Last year i was growing plants with a KH of 7 and GH of 9 without problems. GH of 11 is not such a hard water, it's more low-medium hard from my point of view.
You can do a research, some plants will prefer such parameters, other will not but will grow in it nevertheless, maybe slower.