Help! Dead gourami, another one sick now too!

[slroo]

I have a 55g tank running since February. Water quality has always been good, right now it is Amm0, Nitrites 0, Nitrates 20, PH 7.0, temp 80.
Two days ago my dwarf blue gourami died, he had been listless with slightly (almost unnoticeable) sides, and white/clear stringy poo. Now my flame dwarf gourami is having the same symptoms. I just read that it may be an internal bacterial infection, but I don't understand how it came to be or what I need to do to help him. The other fish in my tank are 4 black skirt tetras, 7 harlequin rasboras, 5 marbled hatchets, 6 dwarf cories, 2 bosemani rainbows, and 4 ottos. They all seem fine at the moment.
I do water changes and vacuum the substrate at least once a week, sometimes more. I use a python, so don't have any idea how much water I'm taking out, but water always looks clear.

 

[severum mama]

Sorry to hear about your loss. Your water perams are good and your tank is not overstocked, so I don't think that is the cause of your problems. If your gouramis have white stringy poop, that sounds like an internal parasite to me. Although I don't have any direct experience treating for parasites, I have seen many of our members recommend an anti-parasite food (I think Jungle brand makes one) as long as your fish is still eating. If the fish won't eat, you could try Parasite Clear tablets- I think that's the name. Good luck!