I have a few different siphons for my tanks for that reason in the last few years I’ve become very paranoid about cross contamination so some siphons I only use for certain tanks, this particular Flowerhorn has his own siphon for his tank never been used for my other tanksLooking at some of anzo1993 other tanks, and fish - any chance of cross contamination? You've had some recent health issues in other tanks, something as simple as using the same water siphon could potentially introduce a pathogen to a tank where the fish is more susceptible, such as your FH.