Apistograma with very strange disease

[Gabs apistos]

Hello everyone!!! two weeks ago i bought a beautiful male apistogramma cockatoo, he swam everywhere, scoured the bottom and played with the otocinclus, but three days ago he started getting close to the surface, when he goes down to the bottom he starts rubbing himself in the gravel very quickly and after that it goes up again and it spins close to the surface, since when I bought it it seems to eat the flakes and expel most of it through the gills, but it has gained weight since it arrived, it has a grayish stain from the store, what can it be to be? to something I can do? the aquarium has 75 liters (20 gallons) is planted with ph 6.6 and temperature 27 degrees (80 faireheits), it lives with 4 otocinclus and 1 BN pleco, yesterday I had a water change and applied a fungicide and bactericide but it didn't work.

 

[MacZ]

As few people here are looking at disease cases I would like to refer you to the forum of fishlore.com

Over there many people help with things like that.

If you should decide to go there copy this template and aswer it as completely as you can.

If you want people here to look at your fish this will also help to copy, paste and answer here.

Also pictures help a lot. Descriptions are usually too general.