Yup, it sounds like you’re neon gobies got reinfected when you returned them to the main tank (neons are completely compatible with seahorses but can sometimes be real ich magnets!). Seahorses have some built-in resistance to ich, as we’ll discuss below, but they can indeed contract this all too common disease. Rather than confining the seahorses in an uncycled quarantine tank while you treat the outbreak of victim your main tank, you may want to consider treating your tank with hyposalinity and acclimating your new seahorses directly to your main tank once you’ve adjusted the salinity to the desired level.
Here is some information on Cryptocaryon from my new book that discusses the life cycle of the parasite, the traditional treatments for ich, and how to treat it with hyposalinity or osmotic shock therapy (OST):
Cryptocaryon irritans (Saltwater Ich, a.k.a. White Spot Disease)
Cryptocaryon is another protozoal parasite that invades the gills and burrows into the skin of marine fishes, including seahorses. The life cycle and modus operandi of Cryptocaryon are very similar to that of Amyloodinium, so it should not be surprising that it also produces strikingly similar symptoms. Infected fish show labored breathing, excess mucus production, and scratch themselves against objects. Along with the characteristic pinhead-sized white spots and excess mucus production, affected fish sometimes show cloudy eyes and secondary infections (Basleer, 2000). The latter can result in skin rot and fin rot accompanied by red or pale patches on the body of the fish (Basleer, 2000).
The white spots seen on infected fish are the adult stage of the parasite, known as trophonts (Basleer, 2000). When they mature, they fall off the fish and encyst themselves. The encapsulated parasites are known as tomonts (Basleer, 2000). Well protected within these cysts, the tomont stage cannot be killed by any medications. The encapsulated tomonts divide into hundreds of daughter cells, which develop into small, ciliated, free-swimming parasites, called tomites (Basleer, 2000). When the cysts rupture, the motile tomites swarm out to seek a new host. In the aquarium, they reinfect the same fishes, and bore into the mucosa of the skin, gills, and fins of their hapless hosts. Once embedded in the tissue, they mature into typical trophonts, appearing as pinhead-sized white spots on most fish, and start the cycle of infection all over again (Basleer, 2000). It is these heavy infestations that can overwhelm even healthy fish.
The free-swimming stage of their life cycle is Cryptocaryon’s one great weakness. The motile tomites are vulnerable and exposed. Ozone or UV can destroy them, they can be killed by all the usual chemotherapeutic agents, and they explode (lyse) when exposed to freshwater and low salinity. It is therefore the tomites that the aquarist must target when treating Cryptocaryon.
At 100x magnification, Cryptocaryon parasites can easily be identified in skin and fin smears. They appear as large, dark, bell-shaped or conical organisms measuring about 350-400 micrometers in diameter (Basleer, 2000).
Outbreaks usually coincide with the introduction of new specimens or environmental insults such as rapid temperature fluctuations (heat stress or chilling), ammonia or nitrite spikes, or a sharp drop in pH (Basleer, 2000). The first step toward treating Cryptocaryon is therefore to restore water quality. Check your aquarium parameters and administer water changes as needed.
The traditional treatment is similar to that for Amyloodinium. Combination drugs such as formaldehyde/copper sulfate or formaldehyde/malachite green are often more effective than copper alone (Basleer, 2000). Medication must be maintained at therapeutic levels for at least 8-10 days and the best results are obtained when daily freshwater dips are a part of the treatment regimen (Basleer, 2000). The entire tank should be treated and methylene blue can be added to the water to aid the breathing of the fish (Basleer, 2000). Be aware that these medications will impair your biofilter and kill your invertebrates!
Cryptocaryon is normally easily distinguished from Amyloodinium by the fact that the embedded parasites produce pinhead sized white spots that are much larger that the tiny dust specks that indicate Marine Velvet. However, the telltale white spots are again often entirely absent when seahorses are the hosts, leaving the seahorse keeper in a quandary when it comes to diagnosis and treatment.
Okay, that’s the story on Cryptocaryon. Seahorses tolerate all the usual treatments for it — copper sulfate, formalin/formaldehyde, malachite green or combinations thereof — but rather than treating your tank with any of these chemotherapeutics, which may damage your biofiltration, and then enhancing their effectiveness with daily freshwater dips, I recommend treating your aquarium with hyposalinity instead. Hyposalinity is a well-established treatment for Cryptocaryon, and basically acts like a permanent freshwater dip. Here is some additional information on hyposalinity and the alternate treatments give you an idea of which option is best for you.
While the usual hemotherapeutic treatments can be effective if carefully and properly administered, they are somewhat risky procedures with a number of drawbacks. Copper, formalin and malachite green can be very harsh on the fish and on the biofiltration. If they are not maintained at adequate concentrations, they will not kill the parasites; if overdosed, they will kill the fish as well as the parasites. They cannot be used with invertebrates and maintaining the proper treatment levels — enough but not too much — for weeks at a time becomes tricky to say the least. It’s a lot like walking a tightrope — lean a bit too far in either direction (too little or too much) and disaster results. The biofiltration is adversely affected and the aquarium may have to be recycled afterwards to restore the population of Nitrosomonas and Nitrobacter bacteria.
Fortunately, there is a much safer alternative that eliminates these problems and which is equally effective against most ectoparasites (Uronema may be an exception), including Cryptocaryon or saltwater ich. It is called Osmotic Shock Therapy (OST) or hyposalinity for short.
Hyposalinity or Osmotic Shock Therapy (OST)
Protozoan parasites cause more illness and deaths among seahorses than many hobbyists realize. This is because, due to their usual anatomy, seahorses often do not exhibit the same symptoms when infected with parasites that normal fishes do. Heavy mucus production and labored breathing are characteristic of the early stages of many protozoan parasite infections such as Brooklynella hostilis, flagellates like Costia and Cryptobia, ciliates such as Uronema, and of course, the marine aquarist’s old nemesis, Cryptocaryon and Amyloodinium. These parasites attack the gills and skin, and fishes typically react to the irritation this causes by ”flashing” or scraping themselves against objects. When seahorses are the hosts, you will often see them attempting to scratch their heads or gills with their tails (Giwojna, Dec. 2003). That scratching will make it clear that the seahorse is suffering from parasites. However, pinpointing which parasites are at work is much more problematic, not does the seahorse keeper always receive an obvious sign of infection like scratching to aid his diagnosis. When seahorses are the host, infections of protozoan parasites are often masked.
This is because the external anatomy of seahorses — an exoskeleton combined with copious body slime — gives them some built-in resistance to protozoal parasites. For example, the ectoparasites that cause ick and velvet ordinarily cannot penetrate deeply into the seahorse’s slime coat and burrow into the underlying tissue, so the telltale white spots often never appear on our armor-plated equines (Giwojna, Dec. 2003). Their gills are still vulnerable, of course, but with the rest of their bodies somewhat protected, seahorses are relatively lightly infested during outbreaks. As a result, seahorses — particularly hardy captive-bred specimens — will often shrug off an outbreak of ick or velvet initially and resist parasitic infections very well, if healthy. But once introduced into the aquarium, the parasites are still present in the system nonetheless, and low-level infections can flare up again to cause problems again whenever the seahorses are stressed thereafter by ammonia/nitrite spikes, a drop in oxygen levels, pH shifts, high nitrate levels, summertime water temps creeping up into the 80s, or whatever.
When that happens, the seahorses will often begin to exhibit a number of unusual symptoms such as “weak snick,” which I have discovered are commonly associated with protozoan parasites that initially attack the gills. I have often seen weak snick as a result of masked infections of Cryptocaryon or Amyloodinium, but the other parasites (Brooklynella, Costia, Uronema) mentioned above have also been implicated in many such cases (Giwojna, Dec. 2003). From the gills, their initial site of attack, these parasites may then spread to involve the throat and snout. As their numbers build up in the gills, they spread from within, invading the esophagus and oral cavity, and I believe such parasites are responsible for several poorly understood afflictions of seahorses such as huffing, hunger strikes/loss of appetite, trigger lock/sticky trigger, and snout rot, as well as weak snick (Giwojna, Dec. 2003).
Fortunately, when such problems crop up, we needn’t determine which particular parasite is plaguing our seahorses, since hyposalinity or Osmotic Shock Therapy (OST) is a very safe treatment that is effective against protozoans and ectoparasites in general. OST is totally noninvasive and harmless to seahorses and other fishes, can be administered safely in the display tank rather than a hospital tank to eradicate the protozoan parasites from your system, and is completely compatible with UV and any medications you may be using (Giwojna, Dec. 2003). OST is therefore the treatment I recommend for problems with external parasites.
OST is totally noninvasive and harmless to seahorses and other fishes, can be administered safely in the display tank rather than a hospital tank to eradicate the protozoan parasites from your system, and is completely compatible with UV and any medications you may be using (Giwojna, Dec. 2003). OST is therefore the treatment I recommend for problems with external parasites.
Hyposalinity also helps parasite-ridden fish avoid dehydration and save their strength by reducing osmotic pressure and making it easier for them to osmoregulate. Allow me to explain.
Because the seawater they live in is far saltier than their blood and internal body fluids (Kollman, 1998), marine fish are constantly losing water by diffusion through their gills and the surface of their skin, as well as in their urine (Kollman, 1998). The mucus layer or slime coat of the fish helps waterproof the skin and reduces the amount of water that can diffuse through its surface (Kollman, 1998). However, when the skin is attacked by parasites such as Costia, Cryptocaryon, Cryptobia, Amyloodinium, Brooklynella, Epistylus and the like, this protective barrier is damaged and water is lost at an increasing rate (Kollman, 1998). The affected fish can easily become dehydrated as a result, further debilitating them.
Low salinity is an excellent way to treat most such skin infections, since reducing the salinity helps the fish recover in several different ways. It lessens the risk of dehydration by decreasing osmotic pressure (Kollman, 1998), and reduces the amount of energy the fish must expend on osmoregulation, helping the weakened fish to recover (Kollman, 1998). And if the salinity is dropped far enough, it prevents reinfection and provides the fish with immediate relief by destroying the parasites in the water and on the surface of the skin (Kollman, 1998). At low salinity, water moves into the parasites’ bodies by passive diffusion until they literally burst (lyse). This method of treatment is known as hyposalinity or Osmotic Shock Therapy.
At the first sign of parasitic infection, I therefore suggest instituting a two-pronged treatment regimen immediately: (1) first, administer a freshwater dip to your seahorses to reduce the number of embedded parasites, clear the gills and snout as much as possible, and provide the seahorses with some quick relief, and (2) treat your main tank with osmotic shock therapy, dropping the salinity to 15 ppt (1.011-1.012) for several weeks to eliminate the parasites from your system entirely (Giwojna, Dec. 2003). If your seahorses seem too weak to handle the stress of a freshwater dip, then just get them into hyposalinity water ASAP — no acclimation!
Step 1: Freshwater Dip
A freshwater water dip is simply immersing your seahorse in pure, detoxified freshwater that’s been preadjusted to the same temp and pH as the water the seahorse is accustomed to, for a period of at least 10 minutes (Giwojna, Dec. 2003). It doesn’t harm them — seahorses typically tolerate freshwater dips exceptionally well and a 10-minute dip should be perfectly safe. Freshwater dips are effective because marine fish tolerate the immersion in freshwater far better than the external parasites they play host to; the change in osmotic pressure kills or incapacitates such microorganisms within 7-8 minutes (Giwojna, Dec. 2003). A minimum dip, if the fish seems to be doing fine, is therefore 8 minutes. Include some sort of hitching post in the dipping container and shoot for the full 10 minutes with your seahorses (Giwojna, Dec. 2003).
If you will be using tap water for the freshwater dip, be sure to dechlorinate it beforehand. This can be accomplished usually one of the commercial dechlorinators, which typically include sodium thiosulfate and perhaps a chloramine remover as well, or by aerating the tap water for at least 24 hours to dissipate the chlorine (Giwojna, Dec. 2003).
If you dechlorinate the dip water with a sodium thiosulfate product, be sure to use an airstone to aerate it for at least one hour before administering the dip. This is because the sodium thiosulfate depletes the water of oxygen and the dip water must therefore be oxygenated before its suitable for your seahorse(s).
Step 2: Hyposalinity (Osmotic Shock Therapy)
Osmotic Shock Therapy (OST) involves maintaining the saltwater in your system at a much lower specific gravity than normal: 1.017 is recommended for reef tanks with live coral and invertebrates, while 1.011 (15 ppt salinity) is appropriate for fish-only tanks (Giwojna, Dec. 2003). Essentially, OST simply places the infectious organisms in an environment in which they cannot hope to survive while the host (or infected fish) is unaffected (Hauter, 2004). It is therefore the parasites that are subjected to the shock, not the fishes, which are normally quite content at the prescribed salinities (Giwojna, Dec. 2003). This low salinity method can be thought of as a continuous freshwater dip, and provides basically the same benefits as a 5-10 minute freshwater dip does, only long term (Giwojna, Dec. 2003).
When the salinity in the system is lowered initially, it is done as if performing a normal water change, except that the replacement water is simply treated tap or RO water without the salt (Don Carner, pers. com.). (If the replacement water is RO/DI or other softened source, then a buffering agent should be employed to prevent pH and alkalinity drops; Thiel, 2003.) Make sure the freshwater you add is thoroughly mixed with the remaining saltwater in the tank as you proceed. This will assure that your salinity/specific gravity readings are accurate. The bacteria colony in the biofilter will survive, the fish will survive, but the parasites will not (Don Carner, pers. com.).
By lowering the salinity, we are also lowering the osmotic pressure of the water. The parasites NEED high osmotic pressure externally in order to maintain a normal water balance within their bodies (Don Carner, pers. com.). Reduce the salinity of the surrounding saltwater sufficiently, and water moves via osmosis into the parasites’ bodies until they literally explode (Giwojna, Dec. 2003). As a higher life form, the fish can withstand this treatment very well; invertebrates and parasites cannot (Don Carner, pers. com.).
For best results, I recommend removing your seahorses to a hospital tank or bucket filled with full strength saltwater (1.022-1.025) temporarily while dropping the salinity in the main tank. They can be given their freshwater dips while you are reducing the salinity in the main tank. Once the specific gravity in the display tank has been lowered to the desired level, the seahorses can then be released directly into the main tank without any acclimation whatsoever. They will make the transition from full strength saltwater to hyposalinity wonderful well, without missing a beat, whereas the ectoparasites they are carrying will be subjected to a lethal change in osmotic pressure.
Once you have attained the desired salinity, monitor it regularly throughout the treatment period and add top-off water as needed to maintain the appropriate specific gravity. You don’t want the salinity to creep up again over the weeks due to evaporation.
While they are in hyposalinity, the seahorses should be fed with live shrimp that have been gut-loaded with antibiotics for at least 5 consecutive days in order to protect them from secondary infections. Prepare the gut-loaded shrimp exactly as instructed for metronidazole, Jonah. Nifurpirinol, neomycin, sulfonamide, or nifurpirinol combined with neomycin are the antibiotics that will work best for this. Neosulfex is also a good choice.
Do not hesitate to maintain the hyposalinity for the entire treatment period. OST needs to maintained for at least 3 weeks in order to assure that all of the encysted parasites have reached the free-swimming stage of their life cycle and been killed.
CAUTION! When administering hyposalinity to seahorses, be very careful as you add the freshwater when you approach the target salinity. You do NOT want to overshoot the mark and drop the salinity too far! Seahorses tolerate low salinity very well up to a certain point, but they cannot withstand salinities below 13.3 ppt (specific gravity = 1.010) indefinitely. Salinities below 1.010 may be fatal to seahorses in a matter of days, if not hours.
In the olden days, many attempts were made to gradually convert seahorses from saltwater to freshwater. Hippocampus erectus tolerated these experiments splendidly all the way down to specific gravity of 1.010, but when the salinity was dropped any further, the seahorses all perished (Bellomy, 1969, p7). These experiments were repeated with several groups of seahorses representing different subspecies of erectus, and the results were always the same: fine as low as 1.010 — defunct at 1.009 (Bellomy, 1969, p7)!
Keeping that in mind, it is best to make your target salinity 1.011-1.012 to allow a margin for error, and to transfer your seahorses to a hospital tank while you drop the salinity in the main tank. That way no harm will be done if you accidentally take the salinity down too far in your main tank before readjusting it and hitting your target salinity. And when you return the seahorses from normal salinity in the hospital tank to the main tank at 1.011-1.012, the parasites will be subjected to the greatest possible osmotic shock, leaving them no chance at all to adjust to change in osmotic pressure.
To be safe and effective, administering hyposalinity requires the use of an accurate method for measuring salinity/specific gravity such as a refractometer. If you will be relying on a pet-store hydrometer for your readings, you may wish to consider alternate treatments rather than OST. If you do decide to try hyposalinity using a hydrometer, please observe the following precautions:
(1) Be aware of the temperature at which your hydrometer was calibrated and make full use of conversion charts to adjust your readings based on the actual temperature of the water aquarium water.
(2) Make your target salinity 20 ppt (specific gravity = 1.015) to allow for a greater margin for error.
(3) In addition, when administering OST it is important to monitor your ammonia and nitrite levels closely at first. Hyposalinity may temporarily impact the nitrifying bacteria in your biofilter, so check your readings closely to see if there is a spike once you’ve reached your target salinity. If so, a simple water change will correct the problem and your biofiltration will be back to normal shortly.
(4) The hobbyist should also bear in mind that hyposalinity can delay gonadal development in immature seahorses and may also prevent mature seahorses from breeding until the salinity is returned to normal. So don’t maintain low salinity for the long term — as soon as the 3-4 week treatment period is over, bring the specific gravity in the main tank back up 1.024-1.025.
When you are ready to return the system to normal salinity, simply empty the tank to about the 1/4 mark and gradually refill the aquarium with high-salinity saltwater. Do this slowly and methodically, the slower the better, taking care not to stress the seahorses unduly. Replace about 20%-25% of the tank’s volume at a time with high-salinity water until the proper salinity range is again achieved (Don Carner, pers. com.). Most hobbyists prefer to use saltwater with a specific gravity of around 1.035 for this (Don Carner, pers. com.), since that will assure that the display tank is restored to normal salinity relatively rapidly, often within a single day. Adjusting the salinity upwards too quickly risks dehydrating the fish due to the increasing osmotic pressure.
If your tank contains corals or delicate invertebrates, or you just want to be extra cautious with your seahorses as they recuperate, adjust the salinity more slowly. This can be accomplished by making smaller water changes, which will require more steps to raise the salinity back to normal, or by reducing the specific gravity of the high-salinity replacement water somewhat. Make the adjustment back to normal salinity as gradually as necessary in order to be confident that you are not stressing the specimens. The hyposalinity should already have done its job so you can afford to be cautious when readjusting the salinity. Take all the time you want.
To be absolutely certain that things go smoothly, take advantage of the online Salinity Adjustment Calculator at the following web site: http://saltyzoo.com/SaltyCalcs/SalinityAdjust.php
This calculator takes the amount of water in your system, your current salinity, the salinity you’d like to achieve, and the maximum change in salinity that you are willing to risk per water change into consideration and performs the necessary calculations. It then returns the number of gallons and salinity of the water for each change (Taylor, 2001b).
The low salinity system was initially developed at the Instant Ocean Hatcheries in the 1980’s and has since been perfected by other large-scale operations (Giwojna, Dec. 2003). Thomas Frakes at Aquarium Systems recommends this system and Rand Kollman recently conducted a controlled study of the method, as described below (Kollman, 1998):
During the study, fourteen 40-gallon tanks connected to a common filtration system at Kollman’s dealership were run at 15 ppt salinity (specific gravity = 1.011), while sixteen other 30-gallon tanks, connected to their own separate filtration system, were maintained at normal salinities of 27-30 ppt (specific gravity = 1.020-1.022) and served as the control group for the experiment (Kollman, 1998; Giwojna, Dec. 2003). Both systems had identical filtration and were maintained at the same temperature (between 79-80 degrees F), Kollman, 1998.
The test period ran continuously from 1994 to 1997, during which time marine fish from the Red Sea, Caribbean and throughout the Indo-Pacific were maintained in both systems (Kollman, 1998). Whenever fish arrived from wholesalers or transshipments, they were divided evenly between the low salinity and the normal salinity (control) system with no acclimation procedures whatsoever (Kollman, 1998; Giwojna, Dec. 2003). No differences in behavior were observed between the fishes in the two systems during the trial period (Giwojna, Dec. 2003).
The results of the three-year study were dramatic and conclusive (Giwojna, Dec. 2003). Outbreaks of Amyloodinium, Cryptocaryon, turbellarians, and monogenetic trematodes were simply not seen in the low salinity system, and periodic microscopic examinations of skin scrapings and gill clippings confirmed that none of the parasites were present (Kollman, 1998; Giwojna, Dec. 2003). On the other hand, the normal salinity control system continued to have periodic outbreaks of all the above parasites. Furthermore, infected fish from the control system were cleared of their parasites within a few days if transferred to the low salinity system (Kollman, 1998; Giwojna, Dec. 2003).
Kollman found the low salinity system reduced his previously high mortality rates and that his dealership was able to greatly reduce chemical treatments and subsequent overdoses (Kollman, 1998; Giwojna, Dec. 2003). He concluded that a salinity of 14 to 15 ppt (specific gravity = 1.010-1.011) was an effective treatment level to which fish can be immediately transferred with no special acclimation procedures (Kollman, 1998; Giwojna, Dec. 2003).
Athough the rapid turnover of specimens at his dealership prevented him from reaching any definitive conclusions about the long-term effects of low salinity on marine fishes, Kollman noted that several fish were maintained in the system for well over a year with no ill effects, and that a Red Sea angelfish (Pomacanthus maculosus) thrived in the low salinity system for three-and-a-half years (Kollman, 1998; Giwojna, Dec. 2003)!
Kollman’s study and the ongoing program at Instant Ocean hatcheries are not the only reports on utilizing low salinity water to quarantine specimens held under crowded conditions (Giwojna, Dec. 2003). As early as 1985, Colorni published a study in Diseases of Aquatic Organism on the effectiveness of hyposalinity in controlling Cryptocaryon irritans in cultured sea bream (Colorni, 1985). Randolph Goodlett and Lance Ichinotsubo have likewise reported their own low-salinity treatment techniques, recommending at least 3 weeks exposure at 14 ppt (specific gravity = 1.010) for a broad range of marine tropical fish species to control various parasites (Goodlett and Ichinotsubo, 1997). They too reported that fish handled immediate transfer into low salinity water "beautifully (Goodlett and Ichinotsubo, 1997)." Variations of low salinity or OST are also gaining popularity among reefkeepers for curing disease outbreaks in reef tanks where copper and other medications cannot be used (Frakes, 1994; Giwojna, Dec. 2003).
Low Salinity Pros (Giwojna, Dec. 2003):
1. Less stressful and longer lasting than freshwater dipping.
2. More effective than freshwater dipping outside the aquaria, since OST kills the free swimming parasites as they emerge from dormant cysts/spores within the aquaria/system as well as those attached to the fish (i.e., the fish are not reinfected once they are returned from the bath to the main tank).
3. No special acclimation procedures required for newcomers.
4. Suitable for all marine teleost (bony) fishes (Red Sea, Indo-Pacific, Florida & Caribbean).
5. Eliminates outbreaks of Oodinium/Amyloodinium (Ick/Velvet/Coral Fish Disease).
6. Eliminates outbreaks of Cryptocaryon irritans (White Spot Disease/Marine Ick).
7. Eliminates turbellarians (Black Spot/Clownfish Disease).
8. Eliminates most ectoparasites, including trematodes, flukes, leeches and Argulus;
9. Prevents the spread of protozoal parasites in general.
10. Reduces the risk of dehydration when the integrity of the fish’ slime coat is disrupted;
11. Helps weakened fish conserve energy and husband their strength by lowering osmotic pressure and making it easier for them to osmoregulate.
12. Reduces dependency on chemical treatments such as copper and formalin.
13. Eliminates the risk of overdoses.
14. Proven to improve the health of marine teleost fishes kept in crowded containment systems with a heavy biological load.
15. Can be used safely with protein, skimmers, ozone, UV, and other treatments.
Low Salinity Cons (Giwojna, Dec. 2003):
1. Sharks and rays are unable to adjust to low salinity systems or tolerate OST.
2. Cannot be used with corals and invertebrates at salinities recommended for fishes.
3. Can be harmful to seahorses at salinities below 13.3 ppt (specific gravity = 1.010).
4. May delay gonadal development in seahorses and prevent breeding until the salinity is returned to normal.
5. Requires an accurate method for measuring salinity/specific gravity such as a refractometer for best results.
6. May not be helpful in cases of Uronema — the most common protozoan parasite infection in seahorses.
7. May impact nitrifying bacteria in the biofilter temporarily.
8. Not recommended for long-term maintenance (this will not be a concern for any fishes that are in the system for 4 weeks or less).
9. Results vary — many hobbyists report great success with hyposalinity; others have no luck using this technique. Much depends on how OST was administered, how low the salinity was reduced and how quickly it was dropped, the accuracy of the salinity measurements, the particular parasite(s) involved and how early treatment was begun.
Invertebrates differ in their tolerance for hyposalinity. Kollman notes that he was able to keep several crustaceans at a fairly low salinity of 18-19 ppt (specific gravity = 1.013 to 1.014). These included arrow crabs, peppermint shrimp, and emerald crabs (Kollman, 1998). Hermit crabs are generally perfectly happy undergoing OST, echinoderms (starfish and urchins) typically don’t tolerate it at all, most shrimp are sensitive, snails vary (Giwojna, Dec. 2003). Nerites and periwinkles don’t mind it at all, others are okay at 1.017 but you can kiss them goodbye at 1.010. Most corals are vulnerable to full OST (Giwojna, Dec. 2003). Reefkeepers and hobbyists with sensitive animals usually do a modified version of OST where they lower the salinity to 1.017 rather than 1.010 (Giwojna, Dec. 2003). The delicate animals generally tolerate 1.017 well and although that’s not as effective in eradicating parasites, a specific gravity of 1.017 is still low enough to provide many of the benefits of hyposalinity (Giwojna, Dec. 2003).
For a standard SHOWLR setup with a clean-up consisting of assorted snails, microhermits, and cleaner shrimp, I recommend relocating the snails and shrimp while treating your seahorse system with full OST at a specific 1.011-1.012 for several weeks. If that’s not practical because it would be too difficult to account for all the snails and/or shrimp and remove them, then I would suggest taking the salinity carefully down to about 1.017 in your main tank, which most of your janitors should tolerate just fine, after moving your seahorses to your hospital tank for treatment at full OST.
Just set up your hospital tank at a salinity of 15-16 ppt (a specific gravity of 1.011-1.012) and adjust the water to the same temp and pH as the main tank. Then administer a freshwater dip to your seahorses, and transfer them directly into the hyposalinity treatment tank afterwards without any acclimation whatsoever.
As I mentioned earlier, OST is completely compatible with most medications. (In fact, many medications are more effective at low salinity than they are in full strength saltwater.) Since secondary bacterial or fungal infections often accompany parasite problems,
If you do not see improvement within 4-5 days of administering OST, don’t hesitate to use the alternative treatments discussed for each particular parasite! They can be administered safely in conjunction with hyposalinity, bearing in mind the impact they will have on the biological filtration, or you can carefully return the salinity to normal and then treat with chemotherapeutics. When administering alternate treatments, check your ammonia/nitrite readings closely, and use water changes as needed to keep the levels of ammonia and nitrite at acceptable levels. Also, you are strongly advised to administer daily freshwater dips in addition to treating with chemotherapeutic agents if the alternative treatments are used in the absence of OST. The freshwater dips will provide the same benefits as hyposalinity and enhance the effectiveness of whatever treatment you employ to control the parasites.
Any of the treatments discussed above can be used safely on seahorses, if administered properly, but I much prefer hyposalinity when Cryptocaryon is the culprit for the reasons we have been discussing. In your case, ecogirl, since the seahorses will be ich-free when they arrive, there is no need for a freshwater dip. Whether you decide to try hyposalinity or not may well depend on what specimens you have in the tank right now.
If you have any qualms about your ability to administer the hyposalinity properly, there are also a few other treatments that are said to be safe for use in reef aquariums with delicate corals and invertebrates, but I have no experience with these preparations personally so I cannot say how effective and safe or unsafe they may be.
Best of luck with whatever treatment you decide to employ, ecogirl!