My fish has a earlier scale lost in that area. I don't know the cause of it but i think it might be the pleco at night searching for food and might got the fish by accident. Than a fews day later i see the block spot on it. Do anyone know wat this is and how to cure it please. I would be greatly thank you and my fish will too. Thank Again!

What kind of pleco do you have with your goldie? How
are your water params?

2 Common pleco and ph is close around 7. Water jus been change 25% and going to vac the gravel tonight last time was 2 week ago. nitrate I m not so sure imma get a test kit for it tmr. Salt added and aquarium plants and specail treatment added in water changes. ( remove Ammonia, chloramine, chlorine, plus nitrate, copper, and most fundus and dieases) (add treament like : lost skin slime, electrolytes)

Oh my, common plecos and goldies are a big NO NO. The
plecos after a time, become carnivorous and go after your
goldies. That and they grow over 12" long. I'll enclose
a pic to show how big they potentially can get.

I would recommend bumping up your gravel vacuums to
once a week. This helps crud from accumulating on the
bottom.

yes the plecos and goldies is no no. but ur fish isnt sick he just has amonia burns. ur water has too much ammonia in it and he got burnt from it. the black is a good sign though it means he is recovering from it. the cure is simply do more water changes. do a 50 % every week fum now on.

Thank you. I m jus gonna get a new tank and let those pleco togeather and get loaches. I told my mom not to get them never like pleco any ways. No offense to thsoe who like pleco. Jus not my type. Loaches are better. I will vac and water change more often and stuff. Plus my ammonia is alway 0 never gotten higher than 1. Thanks You!!!!