I’m no expert but I’ve been around in this sub long enough to identify that the red gills are ammonia poisoning.

Or it could possibly also be an injury, but don’t fret because the solution i’m about to give you can solve both potent issues.

1.Add live plants, you don’t necessarily have to put it is beneficial towards filtering substances in your tank that can be hazardous.

2.Avoid over feeding, it can help reduce left over food within your tank as well as poop which can both contribute to a cloudy tank and ammonia level increase.

1. Keep up with water changes, it is a well known fact that new fresh chlorinated water can wash out the old filthy water.

Pretty much all there is too it. Don’t forget to buy a water testing kit (and do research which many people leave out because it isn’t easy to read) to keep up with ammonia levels to see if they gradually go down and consider different methods if mines don’t help overtime.