so i had a Koi that's about 7 yrs old and about 6 inches long, i had it in a 30 gal
tank and eventually a few months ago added a few new fish (2 small mollies, a small swordtail, a pictus, and a pleco). Then about a month ago i upgraded to a 75 gal
, with new decors like caves and rocks (the old 30 gal
tank only had like 4 artificial plants and 1 real plant). They were all doing fine for a few weeks till i added some new real plants and a butterfly koi. Eventually one of the mollies seemed to be sick and i looked up to what i believe it got the condition where it overeat or what not (i forgot the term) and unfortunately it passed away. My dumb self whos a sucka for good looking fish went and bought these 2 new fish (a small koi and a butterfly koi) and the moment i added them, the big koi have been scared since. at first i thought it was maybe due to bad water (the water was very hazy due to new aquarium which i was fully aware) but a few different tests from stores and a kit i bought showed the water was fine. The staff said its likely due to overcrowded so i did return the 2 new fish back to the store to bring it back to the original number of population but my big old koi is still scared whenever the light comes on or if it sees me come near. It now would only eat if the food sinks down right in front of him. when the lights came on, he would swim drastically around and scratched due to the rock decors, and eventually i noticed the molly start biting him so idk if cuz it knows the big koi is stressed and injured? I now have quarantined the big old koi back to the 30 gal
temporarily and hes doing a bit better but only if light is off. but hes definitely not moving around as much as he used to be. I apologize for the long post and how dumb i sound with the overcrowded part but please any suggestions would help at this point.
p.s the new tank is now seems be very clear after the bacteria bloom phase but even with that, the big ol koi was still scared plus the molly starting biting so thats why i quarantined him. thank you again!