Keep an eye on the one with the ulcer until it is healed. The skin of the fish is a membrane that is between the fish/blood/tissue and the water. A damaged membrane will allow larger quantities of water to enter the fish, diluting the blood. The kidneys try to regulate the internal water level, and if overcome with too much water, symptoms of dropsy, ie pinecone of scales, or popeye will develop. With this size ulcer, it may not overpower the kidneys but you need to be on the alert. If it shows signs of thickening of scales, or popeye, get back with us.
PP can be as effective as Proform C, in my opinion, but it needs to be measured during the entire treatment. It is consumed by organics in the pond, first dissolved organics, then small organics, then larger like parasites, and continue to very large like fish. If it is too strong, the gills can be compromised by being burned significantly, if too weak or too many organics in the pond, then it does not have the strength or longevity to kill the parasites. They do make test strips for measuring the concentration at any point in time. No matter which oxidizer is used, chlorine, PP, formalin, they are all consumed, and all will kill.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard