Blood Parrot Cichlid Died.. Why?

[My3Fish]

Hello.. my blood parrot cichlid, Buzby, died this morning .. and I have no idea why! I haven't done any water changes the last few days, been feeding it it's regular food, the filter was on, heater was on.. I'm confused as to why he died, I have only had him for like 4ish months. About 2 months ago he developed black spots on his body, and I read online that it was more than likely stress spots, and I don't know what caused them because it wasn't like he was being bullied or something, he was the only one in the tank. Then about 3 weeks ago I added 2 electric blue gouramis, and they left him alone, it was more like my cichlid was being kinda aggressive with them, and then about 2 weeks ago I added 2 platys (one was pregnant), which he seemed to like alot until yesterday morning. He started going nuts in his tank. He would go from just being still to swimming crazy fast in his tank, and he kept running into the little platys and running them into the tank walls. Well, I woke up this morning to both of my platys dead and same with my cichlid. I'm just wondering if you could tell me some possiblilities as to why this happened? Hopefully I can learn and not repeat the mistake again..
Thanks..

 

[Spurry]

Personally I would not keep platys with A red parrot cichlid it's a man made hybrid
And agressive It's more than likely kild of the platys (I maybe wrong)
IMO I don't think your stock it very good I would think that it would have needed to be with
Other cichlids to spread out the aggression

There are a few more questions that need to be asked
How long has the been tank running
Did you cycle the filter
What are your current water stats