Hello everyone, I am new here but I am so confused with my tank right now. About 4 months ago I got a tank for the first time (10 gal) and I set everything up and put a betta and a mystery snail in after letting it cycle and everything. Well about a week ago I introduced a clown plecostomus and within a day or two of having him my Betta got sick and was always laying at the bottom of the tank and if he did swim around it was frantic. Also his fins became jagged and somewhat holy but there were no other signs of fin rot. He eats good still, now not as much as he used to but I think he is getting worse. He also seems very scared when he brushes up against something on accident like if someone where to scare you and you jumped. Well exactly 7 days since I brought in the plecostomus he suddenly died. Now I am new so I am worried I don’t have to correct water conditions so we are taking it in to get tested and buying the liquid tester instead of sticks. My plecostomus didn’t act sick at all he was always swimming across the glass of floor and always eating. I will admit that I only fed him once because I hadn’t done enough research but now I do know you should feed them more frequently. He didn’t have anything wrong in appearance so I’m not sure if he was already sick or it was my water or something else. I took him out but before I did my Betta would not go near him and was always frantic if the plecostomus got super close. My Betta is still sick but I did notice that he had turned a little white on his lower half midway into the week near his head and now it is going back to normal. I just don’t know where to go from here. My mystery snail is acting normal but I would hate to try to introduce a new fish and risk hurting the tank even more. If anyone has any idea of what I might’ve done wrong please let me know. I am also new to this so I could’ve done something completely wrong so please just tell me everything because I want to learn as much as possible. I tried to do a lot of research before and sometimes the internet isn’t super reliable compared to other fish owners. Thanks!