Hi BK,
I don't go by dosage on PP. I go with the colour.
Make up a stock solution with 1 tsp crystal pp to 120ml water (or just a small bottle) and shake till disolved.
Wipe tank clean and do a 100% wc (make sure you have the amount of aged water with similar water parameter and temp).
Fill tank back up and drip pp into the tank till tank water turns slightly darker then pink.
You have to have a lot of airation in tank .
Observed the fish for at least half an hr to make sure that they are not stressed (darting aimlessly, floating , lying on side....)
If colour changes to brownish before an hr, drip abit more pp in.
You can treat the fish for at least an hr or leave them overnight.
Always have water on standby just incase you need to do a wc or have some hydrogen peroxide on hand to neutralise the pp.
That is how I do it.
hth,
ron
hth