The congos are in a 75 gallon with a pair of angels (17 congos about 3-4" long)
The blackskirts are in my 100 gallon with a single 7" dempsey, 9 large 6" silver dollars and a pair of 4" angels. I have 15 blackskirts about 2" long. So far they have been in there about 4 months without a casualty. Tons of hiding spots from driftwood, plants...etc. My dempsey is very mellow too which helps.