I have found that metro is more effective in food vs dosing in the water column. You may need to pull those meds out and use general cure if you are dosing in the water column. What you have in the tank is really not a concern, I use live rock as a cave in my qt/observation tanks.
Is he eating, when is the last time he ate, and what was he eating. Prazi pro is usually 1st dose, after about 5 days, water change, then 2nd dose; the 2nd dose is just to kill any eggs. If he had the type of parasites that pp kills, it would usually clear within a couple days or so. Metro deals with thje other type of internal parasites and it has not worked for me in the water column. If he is eating dead food, mix the metro+focus into the food.
If he is only eating live food, do a 25% water change, use some carbon overnight and pull the meds out. Then dose general cure into the water column, it's 2 doses, follow the instructions on the box. If he is eating, feed him good before you dose the general cure, it can play with their appetite sometimes. General cure is pp and metro combined into one med.