Need help with Plecos

Hi everyone... Need some help with plecos experts
I have a L330 and a Peru Green which i just comm with my other fishes
I had mix my L330 a week back but it had white patches but now recovering
I mixed my Peru Green just last Sat and now its also having some white patches and spots... How come its like that can any plecos experts advise?
I did mixed water before adding them in and other fishes are doing fine in there... What should i do now?