German blue rams are impossible fish

I don't know why but for the first time I tried them after 20+ years of keeping fish, they were so weak, died immediately or killed their other. Tried different pH, RO water, higher temperatures, mature tanks with lots of plants, I just had constant issues with them. The last one jumped out after a water change. I've kept marines which are supposed to be 'hard' but never lost any fish apart from one Chromis that someone gifted me.