In general, Seachem recommends using only one medication at a time. Use of multiple medications tends to be stressful to fish to no real additional benefit (there are few infections that require the use of multiple medications at once). All medications are at least a little bit stressful to the fish, and treating with a medication "just in case" means that the fish is probably being stressed for no real benefit. That said, among the Seachem medications only Cupramine will directly interact with other medications, and we strongly recommend to always use Cupramine alone to prevent interactions.
Medication Use Guide
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Red: Do not use these medications together - they will either directly interact or there is no possible benefit to using them at the same time.
Orange: Seachem does not recommend using these medications together, as it is almost never necessary to use both at the same time, but they do not directly interact with each other.
Green: Seachem does not recommend using these medications together if it can be avoided as the use of multiple medications can be very stressful to fish, but there are known situations where it is necessary. It is best to keep one medication in the food and the other in the water if possible.