Your tank is overcrowded. Blue gourami need at least 30-35 gallon tank and the goodea atripinnis are better in a larger tank as well. Catfish and plecos make a lot of waste so a larger tank is better. The sooner you get bigger tanks, the better.
I'm slightly suspicious about your tank being cycled since you have no nitrate readings. It could have been cycled at first, but when you have too much of a bio load, the beneficial bacteria dies off. Could you do another nitrate reading just in case it was faulty?