Santa Cruz Biotechnology sells pure chloroquine diphosphate for $55/25g. Shipping is expensive (express, ambient temperature). At 15 mg/l, this would treat 1,667 l or 440 gallons of water. Seems like a cheap price to pay for all the expense and trouble of keeping delicate fish healthy before the display tank. Helpful link:
https://www.advancedaquarist.com/2013/2/fish
The National Fish Pharmaceutical product is pharmaceutical grade and $50 for 100g. For large systems, Fishman Chemicals sells (according to the owner) USP Pharmacopeia grade chloroquine diphosphate for $190/kg, which would treat over 66 thousand liters. Not sure why more aquarium keepers aren't using this product in quarantine or for treatment given its therapeutic range. Good group purchase opportunity! I have an analytical balance...