I am not trying to be hard on you for following the breeder's advice. To follow the breeder's advice is typically the best course of action. I just felt it important to voice my concerns (and, aparently my ability to "soften" my posts is on the fritz, b/c everything I type lately seems more *um* "snotty" than I intended).
Malachite green and formalin both target parasites. Formalin also has mild anti-bacterial properties, but it isn't going to kill off a bacterial infection. As far as I am aware, nothing available to fish is going to target viruses. Furan-2 will target bacteria, and also fungus to some extent.
On the "covering all bases" subject. I do want to express my concerns that throwing the kitchen sink at a seahorse (or anything else) can squash it.
Antibiotics, antiparasitics, and other drugs are all very hard on the seahorse's renal system. The more you throw at them, the harder it is on them. Back in the day, when people were throwing the highest dose of the strongest meds at the seahorses every time they got sick, the seahorses would appear to get better, only to die shortly down the line, presumably aided by damage to the renal system. Human doctors don't give you several possible antibiotics at the same time whenever you are sick for the same reason. Malachite green is very hard on fish, formalin is very hard on fish, and Nitrofurans aren't exactly a walk in the park. All three is quite a stress load. It does help that she's only being exposed to the MG/Formalin for a short period of time once a day, but it still has me a little worried. And it helps that the others are only being exposed to the Furan, but it's still more than their systems should have to be exposed to, IMO.
I hope I'm not coming across as harsh, or even argumentative. Just wanted to make sure I made clear my concerns for any future person reading this thread.
If any of the seahorses go off their feeding, or begin to show signs of buoyancy problems (especially sinking), those would be cause for concern.