Lee here might be some questions you should help answer for me please.
Did you feed them too much?
Do you siphon the tank?
What type of water do you use?
How big is your filter?
Do you have any aquarium plants?
Have you ever had this problem before?
And
Have you tried Melafix?
I don't know if it will work.. but it helps me a lot with my fishes.
I recommend that if you don't want to use any water conditioner, you can try and use
RO water, you don't need any conditioner for it because it is soft water and all...
Please take my advice on aquarium plants especially if you don't use conditioner, or siphon the tank.
Plants absorb a lot of the nutrients in the water. So like
nitrite or
nitrate.. don't know which one.. but the plants do absorb little bits at a time. They like iron too which makes the leaves green, and fish waste.
I have a female gourami which looks pregnant, and 3 other male gouramis... but I never had any problems with them.