There are a few good treatment options you can consider for an “itchy” seahorse that has begun scratching itself due to external parasites (ectoparasites) when you do not know which particular parasites are causing the problem.
To be more specific, you can treat the entire aquarium using a good antiparasitic medication such as Parinox from National Fish Pharmaceuticals, you can treat the affected seahorse(s) with formalin, or you can administer hyposalinity (Osmotic Shock Therapy) at a therapeutic level.
Here is some additional information regarding the Parinox and the sorts of parasites it is effective in treating:
USE: for ich, Hexamita, costia, ichthyophthirius, ectoparasites, monogenia (trematodes), Hirudinea, parasitic copepods, argulus, Lernaeidae, anchor worms, fish lice, leeches. Also a protozoacide. Antibacterial, antiparasitic — very wide spectrum. Our version of a “cure-all.”
DOSAGE: 1/4 teaspoon per 20 gallons of water. Treat once a week for two weeks. If water changes are done, add back the percentage of the medication according to how much of the water was changed.
And here is some additional information about Kordon Formalin 3, which is the brand I prefer, explaining what it is most effective in treating and how to administer the formalin:
Kordon Formalin 3 treatment instructions
Formalin can be useful in treating fish with the following clinical symptoms:
Increased respiration; loss of normal body color; presence of discrete white spots (freshwater or saltwater “ich”); white areas on the body with circumscribed, reddish perimeter (Epistylis and/or bacterial infection); scratching on tank bottom or objects, lethargy, white cottony tufts or strands on body (fungus); dust-like, “peppered”, yellowish spots on body surface (Oodinium); whitish skin slime or filmy body covering or patches (columnaris disease); disintegrating fins or fin edges (fin rot); mouth “fungus” (bacterial infection); pustules, furuncules or ulcers.
If any of the above symptoms are similar to the problems you’ve noticed with your seahorses upon close inspection, then administering formalin baths to the seahorses may be helpful, Seabiscuit. Formalin 3 by Kordon is the medication I prefer for these treatments. These are the instructions for treating fish with Formalin 3, the Kordon brand of formalin, which is readily available at most fish stores:
SUGGESTED TREATMENT PROCEDURES
The following procedures are suggested for both freshwater and marine systems, unless otherwise noted. It is important to note that some activated carbons can remove formaldehyde from water, but formaldehyde persists for only a few hours in aquariums and does not accumulate in the water.
SUCCESSFUL DISEASE TREATMENT
Successful treatment of diseases of aquarium fishes relies upon several factors. Firstly, as discussed above (“General Diagnosis of parasitic Diseases of Fishes”), a proper diagnosis of the disease must be made, and this can be one of the most difficult tasks facing an aquarist.
Secondly, the start and duration of a treatment is important. A disease which will usually respond to a given medication may not respond if the treatment is started too late, or if the length of treatment is not long enough.
Lastly, the correct medication at the correct dosage must be used with the proper treatment method. Formalin·3, for instance, will not be effective against systemic (internal) diseases of aquarium fishes because the therapeutic effects of the formaldehyde are restricted to those surfaces of the fishes that contact the treated water.
Water changes are another important factor. Some medications state that water changes are not necessary, but the fact is that water changes are always helpful. Depleted dissolved oxygen levels are replenished, dissolved organics are removed as are free-living disease organisms.
Treatment in a separate treatment or hospital tank, if possible, is also important. However, this is often a nuisance and in many cases the entire aquarium population is diseased.
TREATMENT OF FUNGAL AND PROTOZOAL DISEASES OF FISH (LONG-TERM BATH)
(a) Since there is conflicting evidence regarding the safety of formaldehyde to biological (nitrifying) filtration, all long-term bath treatments with Formalin·3 may (at the user’s discretion) be done in a separate hospital or treatment tank.
(b) Remove granular activated carbon from all filters used on the treatment tank; clean or change the mechanical filter media (i.e., filter floss), and return the filter(s) to service (minus the carbon).
(c)Make a partial water change of approximately 25%
(d) Depending upon the condition of the fishes needing treatment (i.e., the severity of the disease, involvement of the gills and the degree of debilitation), the dosage should be varied from 1 to 2 teaspoons per 10 gallons (10 to 20 ppm.) Severely diseased or debilitated fishes should be treated at the lower dosage.
(e) The treatment may be repeated every 24 hours, by repeating all of the above steps, including the required water changes.
(f) The dosage may be increased as the condition of the fishes being treated improves.
(g) If the fishes were removed to a separate tank, the original aquarium or pond should remain devoid of all fishes for a period of at least 4 days to insure all of the remaining infestation has expired.
METHOD 2 (DIP) FOR THE PREVENTION OR TREATMENT OF FISH DISEASES
(a) To a clean, non-metallic container (i.e., a plastic bucket), add one or more gallons of fresh tap water treated with Kordon’s AmQuel . For marine fish use freshly prepared saltwater adjusted to the same specific gravity (or salinity) as in the original tank. Make sure the temperature in the container is identical to that in the aquarium
(b) Add 1 to 2 teaspoons of Formalin·3. This produces a concentration of 100 to 200 ppm. formaldehyde.
(c) Agitate the solution with an airstone and adjust for a moderately strong flow of air.
(d) Remove the fishes to be treated and deposit them in the container for a treatment period of not more than 50 minutes. Immediately after the treatment period, or if signs of distress are noted, remove the fishes to a previously prepared recovery tank. The fishes may be returned to their original tank, but the presence of the original disease-causing agents in the tank water may result in a reoccurrence of the disease condition.
(e) Observe recovering fishes. Make sure that tankmates do not molest them during recovery.
(f) Repeat treatment as needed, every week. Each treatment is very stressful to the treated fishes. Do not reuse the dip solution.
If you are going to use the formalin to treat your seahorses, Seabiscuit, please copy the following URL and paste it in your web browser. It will take you to a webpage with additional information about Formalin 3, and you should read through the information there before you begin the treatments:
Finally, Seabiscuit, you can administer hyposalinity in the main tank. Let me know if that is the option you would prefer and I can provide you with detailed instructions explaining how to proceed, since the level of hyposalinity that is appropriate will depend on the type of specimens you have any aquarium, especially the invertebrates…
Best of luck providing your itchy seahorse with some lasting relief!
Pete Giwojna, Ocean Rider Tech Support