Hi all. My male guppy has been acting weird for a while. He swims slow and stays in one spot a long time. He does interact with the female once in a while. So here is a pic. Can it be fin rot? Can I use sera mycopur for it if it is and is it safe for kuhlis? Water par is 0,0,15
Have you been doing 25-30% minimum water changes every week? That looks like the water quality has deteriorated.
The test kit crew will suggest an immediate test, which could give you valuable info. If you don't have a kit, go onto a vigorous water changing routine. 25% 2 or 3 times a week. That tail should recover.
Throwing antibiotics at it seems unnecessary to me.
It seems to have copper chloride and copper sulfate, which is why I had to look it up - copper meds seem banned in many jurisdictions. It shouldn't be a problem for loaches, although if you really want to use it (you seem to) I'd go at a half dose and watch closely.
Copper is murder to get out once it's in though. Simple water changes won't always do - it lingers.