They're just like any other mbuna, territorial and will be even more aggressive when breeding. Check out the video in my signature, it's my former 55 gallon tank which had a group of Jalo Reef.
My liter to gallon conversion isn't so great, but isn't 20L equivalent to 5G? If so, that's WAY too small for any african cichlid. A trio of mbuna should be in at least a 150L tank, which is 30 gallons or so I think.