Cichlids in a 20 gallon tank?

they are lying. The only cichlids that would ever be okay in such a small tank are things like kribs or blue rams. Anything else would outgrow the tank in less than a year. That one fish inch thing is a bunch of crap. There are other factors, like waste production and swim space that need to be taken into consideration. For example, if that rule applied you could keep a guppy in a 1.5 gallon easy. But you can't. Guppies need a good 1-2 feet to swim around, which means they're going to need more like a 10-20 gal. They also produce quite a bit of waste, so a 1.5 gallon would be way too dirty for them. Territory size also makes a difference, and cichlids are all about their territory. Cichlids, depending on the species, are generally pretty aggressive. If all you have is a twenty gal, no cichlids for you, so there is no point in even answering your last question. (although to answer it, no. Silver tipped sharks also need VERY large tanks).

This would depend on the type of cichlid, you could not have larger cichlids like oscars but you could have some smaller cichlids like a couple angelfish or some rams. I also believe that you could try it out with a pair of yellow or blue lab cichlids or a small mixed species and if they get too big buy a bigger tank for them.

@0 gallons could possibly home some apistogrammas, or some kind of shell dwelling cichlid, 20 gallons is really too small for kribensis or rams, rams are to sensitive and need 30 gallons, kribs get pretty big, and need more room to make territories.