Blue Gourami Can't Float Anymore

[Profchaos71]

Lets start with my setup. I have a 130g long tank. I am running a fluval 406 and two aqua clear 70 power heads. The power heads are on opposite sides of the tank and each runs into its own undergravel filtration thus splitting the tank and the work in half. I have been running an air stone as well,and today I finally hooked up a bubbler to one of the power heads to essentially more than double the oxygen level. I have well water and I do 50 percent water changes usually weekly.i might go a few days longer . I have two 10 inch tiger oscars,a 12 inch Pleco ,and a blue gourami. I bought the gourami almost two years ago in a ten gallon tank,then I bought the oscars together when they were smaller than the gourami. Graduated to a 55,then to my current tank. The oscars never really bother the gourami . Well for awhile now the Gourami has stopped being able to just float in the water. He always had his little spot where he would post up and just float like two inches from the top and of course horizontal. Well suddenly he was constantly swimming straight up,never stopping. If he stopped he would sink,and in fact now he has finally gotten too tired and is just resting on the bottom,pointing almost straight up and occasionally musters the strength to swim to the surface . If you agitate him he can swim straight when he needs to,but then goes right to the bottom . The other fish appear to be normal and let me tell you,I was overseas for a year and my tank didn't get any care and these fish survived that with no problem. I had green algea everywhere and the water was horrible and it didn't faze that Gourami one bit. My water now is crystal clear.
Sorry,somehow the pic posted upside down
My whole tank

 

[the_lock_man]

When did you come back? If it was very recently, your tank might well be suffering from Old Tank Syndrome - with no care, the nitrate levels will have built up to ridiculously high levels, and the fish got used to it, as it increased gradually. Then you came back, clean the tank up, give it some nice fresh, nitrateless water, and the sudden lack of nitrates has shocked the fish.