Prazipro uses oxybispropanol to keep the Praziquantel in solution. Oxybis uses O2 from the tank water sometimes at an alarming rate. The fish begin to suffocate from lack of O2. When using Prazipro the amount directed on the bottle is a bit strong at 2.5 and works well at 2.0. But because of the oxybis, it is important to run a good strong powerhead aimed up at the surface where it is actively rippling the water surface. This creates a strong exchange of O2. Also a good idea to run a foam bubbler or airstone to augment the powerhead. While Prazipro claims to ok to use in a reef tank, it can cause deaths of feather dusters, bristleworms, etc. Plus, as Vetteguy posted, you need to take into account the actual gallons of water in your tank. A 100 gallon tank for example is not a full 100 gallons. Need to measure it by filling with buckets or using one of the many online calculators to determine actual gallonage. So you may have experienced a combination of several things going badly in your tank: fish probably had flukes which when dosed with prazi can spasm hurting the fish's gills and ability to transpire O2; the oxybis robbing O2 from the water; and possible overdosing due to measurement.
Sorry for your losses. So many beautiful fish
