I've got a midas, salvini and JD in a 50gal all of which are around 8inch and they are fine.
That's really not fine... unless your running a really good canister or sump then the bioload in there is going to be huge, and thats not even the big problem. like xinchavoc said those fish are probably stunted. Midas get to be over a foot long normally its not uncommon to see them that big, but it is uncommon to see a Midas that stopped growing at 8inches.. That tank is really only big enough for your JD or your Salvini... not all three, not even two of them, and definitely not a Midas not even if it was by itself.
, if you could figure out how to utilize the search function here on MFK, you could find thousands of setups and also find answers to all your other threads youve posted that have been answered thousands of times since 2005.