Rats! I hate to hear that your female didn’t make it, but things were sounding very grim based on your last report. She must have been awfully, awfully weak to be resting prone on the bottom and barely able to fend off an attack by a bristleworm. All my condolences on your loss, sir!
If it’s any consolation, I don’t think you had any option but to attempt an emergency transfer to the hospital tank under the circumstances. If the bristleworms were already taking an unhealthy interest in her, like vultures maintaining a vigil over their dying victim in the desert, she never would have survived the night in your main tank once the bristleworms came out in full strength after lights out.
Yes, sir — it would be very prudent to line up some of the most useful medications to keep on hand just in case they are ever needed. Furan 2 is a good combination medication to keep in your fish room, and if you will do a quick search of this forum for the phrase "medicine chest," you will find a detailed discussion of other medications that are very useful and can comprise a first aid kit for the seahorse keeper. Just type in "medicine chest" in the search window in the upper right-hand corner and press "Enter" on your keyboard.
In the meantime, keep the five-gallon hospital tank you set up running to serve as a hospital ward-quarantine tank in the future. Install a sponge filter to provide some biological filtration for the tank when you’re using it to quarantine new specimens or to treat ailing specimens with medications that won’t impair the biofilter. And I would adjust the water in the hospital tank to the proper level for hyposalinity (1.011-1.012 if you have a refractometer or about 1.015 if you’re relying on pet shop hydrometer to measure specific gravity) and maintain it at that level for best results.
Since you’ve lost seahorses with similar symptoms in the past 2-3 weeks now, I would also give serious consideration to installing an ultraviolet sterilizer on your seahorse enclosure, Don, as discussed below:
Although it does not improve water quality to nearly the same degree as an ozonizer used in conjunction with a protein skimmer, UV radiation in the proper range (295-400 nanometers) is known to help oxidize phosphates, metabolites, organic molecules and nitrogenous compounds through the incidental production of ozone (Fenner, 2003a).
The primary benefits UV sterilization provides, however, are disease reduction and the reduction of nuisance algae. Ultraviolet radiation can be very effective in reducing free-floating algae, bacteria and microbes in general, certain parasites while in the free-swimming stages of development, and other suspended microscopic organisms (Fenner, 2003a). Seahorses are prone to a number of serious bacterial problems such as Vibriosis, and a properly installed and maintained UV sterilizer can be invaluable in reducing the incidence and spread of such infections. When properly used, UV sterilization can reduce microbial levels in the aquarium to the low levels normally found in the wild or below (Fenner, 2003a).
For best results, the UV sterilizer must be properly sized, operated, and maintained. In order to provide a good kill rate per pass, the effective dwell time (the length of time the water is exposed to UV radiation while passing through the sterilizer) should be maintained at or above roughly twenty gallons per hour flow per watt of UV (Fenner, 2003a). This sounds complicated, but selecting the right sterilizer for your needs is actually very easy. Every manufacturer provides guidelines to help the hobbyist choose a unit and a pump that provide the proper wattage, flow rate and exposure time for any given application.
To assure efficient transmission of the proper wavelengths, sleeves (i.e., the quartz jacket that shields the lamp) must be kept clean and UV bulbs must be replaced at regular intervals. Equally important, the aquarium water should be filtered before it passes through the sterilizer. For maximum efficiency, make the UV sterilizer the final component of an in-line filtration system, so that the water has already passed through your mechanical, biological and chemical filtration media before it flows through the sterilizer (Fenner, 2003a). Do not operate your UV sterilizer during the break-in period when a new aquarium is being cycled and the biological filtration is becoming established. It is counterproductive to reduce microbe levels and nutrient levels when the aquarium is cycling.
Ultraviolet sterilizers are not necessary for maintaining seahorses, but nowadays I would not attempt to keep wild-caught seahorses without one. Hardy, disease-resistant farmed-raised seahorses can do just fine without them, and reefers often frown on UV because it reduces the population of microscopic planktonic organisms filter-feeding invertebrates require. But in my opinion a UV sterilizer makes a very useful addition to the filtration system of the average seahorse setup. The fish farms and aquaculture facilities that raise captive-bred seahorses employ UV radiation in their nurseries and grow-out tanks, and there is no reason the home hobbyist should not take advantage of this technology as well.
Good luck assembling a basic first aid kit for your seahorses, sir!