Fish dying...

I have, well had 2 medium size cichlids (one orangish, and one blue and black, almost purplish, sorry i don’t know the species name.) in a 30 gallon tank(i know, I was looking for another tank for one of them.) with a great filter, water changes regularly and feed normal. At first the orange fish seemed to lose its site and run into stuff, after 3 water changes it was back to normal. How ever the blueish fish started to act very crazy and run into things at a high speed and just tear its self up. I put melafix in the tank which helped it until two days ago when the fish was laying on its side on the bottom of the tank and trying to move but couldn’t. That fish died less than 4 hours later. Now the orange fish is showing the exact behavior but when I got home today it too was in the same spot on its side on the bottom. Is there anything I can do to save it or am I too late? What could cause this?

Thanks in advance for the information and for reading.