While on holiday a relative came in a fed my fish, on my return the tank was in a mess, I think she way overfed, despite going through everything with her. I did an immediate water change and the next day parameters were fine. I've now noticed one of my Amano shrimp has a stark white patch just behind its head and there is a lighter strip running down its back. It's eating well and moving around but I'm really worried its got the start of muscular necrosis. I don't have a spare tank to quarantine and I really don't know what to do. I've read that regular water changes can help, but is that daily? Any advice please? I tried taking a pic but its not very clear. I have 4 shrimp in total.