So I have a 50g with three Pearl Gourami and four Amano shrimp. I’d like to add by some small schooling/shoal fish. Problem is my tap water. Out of the tap nitrates are 40ppm or worse if farmers are fertilizing their fields. Furthermore, my water is ridiculously hard. GH and KH in double digits. All my fish have adapted to this (I also have a 29g). I need a fish that’ll be able to do the same. Suggestions?