I just lost half of a very rare (and expensive) tank to I don't even know what. Filters are running fine, temperature, pH, Nitrates, Ammonia all on target... I'm getting ready to take out a voltage meter and check for a voltage leak in the tank. It sucks. I'm sorry for your loss and give you credit for not just wanting to kick it all to the curb.
Right now I have the young kribensis and chocolate cichlids in 20 gallon high tanks to grow them out.
I have 3 large chocolate cichlids in my 210 gallon tank (along with other fish), and they get fairly big as adults (up to 12 inches and thick). I wouldn't put a pair of full grown chocolate cichlids in less than a 55 gallon tank myself (assuming excellent filtration), and many would say even that is pushing it. For my 210 gallon tank, I have an FX6 canister filter, a SunSun canister filter, and 4 large Hydro-sponge filters and I do 80% water changes every 1-2 weeks.
Kribensis are dwarf cichlids and only get 2-3 inches long max, so if you have a smaller setup those would be a better choice.