My rams (erfly cichlids) are dying over period of 2 months one by one,?

Rams are notorious for carrying internal parasites, and I'd guess this is what you're seeing. The only external signs would be reclusiveness, darkening color, and possibly swelling or sinking of the abdomen (as the parasites either multiply enough to cause swelling, or starve the fish to cause emaciation). If they're still eating, beging lacing their food with metronidazole based medications (Flagyl, Fish Zole, Metronidazole, Hex-a-Mit, etc.), as this will treat the issue directly. If they refuse to eat, treat the water with any of the above-listed medications-- this is less effective, but your only shot.