Yes, that’s correct — continue to treat with the Furan2 for 10 consecutive days. One of the packets is the proper dosage for a 10-gallon hospital tank. Each day you will need to perform a water change in order to maintain good water quality and keep the ammonia from rising to a dangerous level. If you change 50% of the water (5 gallons) each day to control the ammonia, then you need to add 50% of the recommended dose of the medication after performing the water change, which would be 1/2 packet of the Furan2. If you needed to change all of the water in the hospital tank weapons (100%) in order to control the ammonia, then you would need to add an entire packet of the Furan2 afterwards to maintain the proper dose.
The methylene blue is safe to use with the Furan2 and will help to darken the aquarium water and protect the photosensitive medication from being deactivated by light. You can add more methylene blue each day following the water change, if necessary. I would add the methylene blue drop by drop, using just enough to give the water in the hospital tank a nice blue tint, but without darkening the tank so much that it is difficult to observe the seahorse clearly, or so that the seahorse has any difficulty targeting its prey and feeding normally.
Some hobbyists will feed the seahorses adult brine shrimp that has been soaked in Furan2 in addition to adding the medication to the water in the hospital tank, and report good results with this method of treatment. The Furan2 is known to be more effective when it is administered orally, and the live adult brine shrimp also help stimulate the seahorse’s feeding instincts, so don’t be afraid to feed your pony medicated adult brine shrimp in addition to treating the hospital tank.
Best of luck with the treatment regimen, Julie! Here’s hoping that big Bertha is soon back to normal again.