Okay, sir, if your stallion has developed positive buoyancy, then we can be confident that he is suffering from internal gas bubble syndrome (GBS), which causes the swimbladder of the seahorse to become hyperinflated and/or gas to be released within the coelomic cavity of the seahorse. If the seahorse is still eating, then administering Diamox orally can be helpful in treating this condition, but it is a difficult problem to resolve and the most dangerous form of GBS a seahorse can develop. I will explain the best way to use the acetazolamide (brand name Diamox) in a case like this later in this message, Tom, but first let’s discuss internal GBS in a little more detail and go over all of the treatment options that are sometimes helpful for treating this problem.
Gas bubble disease is not at all contagious; it isn’t caused by any sort of pathogen, so you needn’t be concerned that it is going to spread to the rest of your herd like an infectious disease, Tom. Since it is not actually a disease, I prefer to refer to gas bubble disease as a syndrome and call it gas bubble syndrome (GBS). Even though it is not an infectious disease, the rest of your seahorses are still not out of the woods, sir. GBS is an environmental disease that is triggered by certain conditions within the seahorse tank itself, so you will need to correct the conditions in your aquarium or the rest of the seahorses could also be at risk. (Because of their heavily vascularized, physiologically dynamic brood pouch, mature males that are actively courting or breeding are the most susceptible to GBS.)
One of the measures that sometimes helps with internal GBS is to pressurize the seahorse at depth in a tall container, Tom. As a rule, the deeper the container and the greater the hydrostatic pressure at the bottom, the more effective recompressing and then decompressing the seahorse will be in relieving this type of problem.
You can also consider partially deflating the seahorse’s swimbladder by performing a needle aspiration in order to help relieve the positive buoyancy, and treating the seahorse with Diamox orally can be helpful if the seahorses still eating. I will explain all these options in more detail for you below:
As you know, the swelling in the chest and abdomen of your seahorse is due to a different form of gas bubble syndrome. When the gas emboli that trigger GBS form in the capillary network of the gas bladder (the rete mirabile), hyperinflation of the swimbladder occurs, resulting in positive buoyancy. And when intravascular emboli occur deep within the tissue and occlude blood flow, generalized edema results in the affected area. Or extravascular emboli may cause gas to build up within the coelom, often resulting in positive buoyancy and swelling or bloating of the abdominal cavity (internal GBS).
That’s what’s I believe is happening to your stallion, Chris. New gas emboli have formed and are either causing the gas bladder of the seahorse to become overinflated, or are causing gas to build up within the coelomic cavity of your male, or both. This condition is known as internal GBS, and it is much more difficult to resolve successfully then external GBS (i.e., tail bubbles), chronic pouch emphysema or other forms of GBS.
There are a few treatment options in such cases:
(1) First of all, you can try manually deflating your stallion’s gas bladder. If the bloated chest and abdomen he has developed is due to a hyperinflated swimbladder, releasing some of the excess gas and partially deflating the gas bladder may provide him with relief and counteract the tendency to float.
(2) Secondly, you can try pressurizing him at a depth of at least 40 inches in a homemade decompression chamber.
(4) Thirdly, you can try treating him with the Diamox orally, if the seahorse is eating, or Diamox plus antibiotics in a hospital tank, if the seahorse is no longer eating and the Diamox cannot be administered orally.
The simplest of these is to manually deflate is swim bladder using a hypodermic, which is a procedure we’ll discuss in more detail below.
Manually deflating the swimbladder is accomplished much like a needle aspiration, except the needle is inserted into the gas bladder rather than the pouch. This is how Dr. Marty Greenwell from the shed aquarium describes this procedure in the 2005 Seahorse Husbandry Manual:
"If a hyperinflated swimbladder is suspected, a bright light can be directed from behind the animal to visualize the location and borders of the distended organ. This is useful when attempting to deflate the bladder. The needle should be directed between the scute/plate margins for ease of penetration through the skin. The external area can be rinsed with sterile saline or a drop of triple antibiotic up all my appointments can be applied prior to penetration."
The seahorse’s swimbladder is a large, single-chambered sac that begins in the band of its neck and extends 1/3 of the length of its body cavity along the dorsal surface. It’s a large organ so if you can visualize it clearly using a bright light (just like candling an egg), releasing some of the gas to partially deflate the swimbladder is fairly straightforward and uncomplicated.
Here is a e-mail from Lindsay Parker at the Monterey Bay Aquarium explaining how they use this procedure to restore normal buoyancy when their prize leafy seadragons have problems with positive buoyancy:
Recently we have had issues with Leafy Dragons becoming buoyant. The most common scenario is that we arrive in the morning to find an animal floating at the surface, on its side, often swimming in a circular pattern. By candling the animal we confirm that the swim bladder is enlarged and then aspirate the extra gas out of it using a small syringe. The aspirated volume depends on how over expanded the swim bladder seems, typically though it ranges from 1cc-2cc. At that time we also begin an injection series, a combination of Acetazolamide and Ceftazidime, and often end up tube feeding.
Animal Husbandry Department
Monterey Bay Aquarium
886 Cannery Row
Monterey, CA 93940
If the problem is a hyperinflated swimbladder, this simple procedure will provide your seahorse with immediate relief and cure the problem. But if you cannot make out the swimbladder clearly or if the problem is due to excess gas building up within the abdominal cavity, rather than a hyperinflated gas bladder, then pressurizing the seahorse a homemade decompression chamber is often your best bet for a good outcome, as I will discuss with you in more detail below.
In my opinion, Internal GBS is often best treated by recompression-decompression, which causes the emboli or gas bubbles to go back into solution and be resorbed, so that’s also something you should strongly consider, Tom. In your case, I would suggest pressurizing the affected seahorse in a homemade decompression at a depth of at least 40 inches as described below. If you think it would be helpful, he can be treated with antibiotics and Diamox while he is undergoing the decompression cure to help him recover from any infection that may be involved. External GBS typically responds extremely well to treatment with Diamox, but internal GBS is a much more serious condition, and often responds better to pressurization, in my opinion. But if you can combine the pressurization with antibiotic therapy and Diamox, that will increase the chances of a good outcome.
Internal Gas Bubble Syndrome (GBS) is the most dangerous form of this affliction because any of the internal organs in the abdomen can be affected by the gas emboli that form in the seahorse’s blood and tissue, yet there are no outward indications of trouble at first, making it difficult to detect the problem until the condition is well advanced and serious damage has been done. The gas emboli occlude vessels and capillaries, thus restricting the blood flow to the affected area, which is what makes the internal form of GBS so insidious — irreversible damage can be done to vital organs or organ systems before sufficient excess gas builds up within the coelomic cavity to cause positive buoyancy and alert their keeper to the problem.
Carbonic anhydrase inhibitors such as Diamox, which work so wonderfully well when treating external GBD (subcutaneous emphysema), are not as effective in reversing this type of damage, but can be helpful if combined with antibiotic therapy and pressurization.
When treating internal GBS, the outcome often depends on which internal organs were involved and how soon the problem is detected. In my experience, the prognosis and chances for a successful outcome are much better when treatment is begun while the seahorse is still eating. Unfortunately, that can be difficult to accomplish when you’re dealing with Internal GBS because the seahorse remains largely asymptomatic until it becomes bloated and begins to float.
In my opinion, Internal GBS is often best treated by recompression-decompression, which causes the emboli or gas bubbles to go back into solution and be resorbed. It works especially well when hyperinflation of the swim bladder is part of the gas bubble syndrome, since the increase in hydrostatic pressure triggers the capillary-rich oval of the swimbladder to begin resorbing excess gas. Equally importantly, the recompression-decompression cure is an excellent option option for treating Gas Bubble Syndrome (GBD) for hobbyists who are having trouble obtaining Diamox for one reason or another or for seahorses that are suffering from internal GBS. Anyone can set up a simple homemade decompression chamber and begin treating their seahorse as soon as they can mix up a new batch of saltwater. If you want to give it a try, here is how to proceed, Tom:
The Recompression Cure for Gas Bubble Syndrome
Recompression simply involves placing the affected seahorses in a flow-through cage or enclosure and immersing them for a period of days at a depth with sufficient water pressure to cause the emboli to dissolve. The increased hydrostatic pressure causes the gas bubbles that have formed within the tissue and blood of the seahorse to go back into solution where they can be resorbed, relieving the problem. (This is why a decompression chamber is used to treat divers for the "bends," caused by nitrogen gas embolisms within the diver’s tissue and blood.) Afterwards, the seahorses are slowly raised back to normal depth/pressure over a period of hours, allowing the total partial pressures of the dissolved gases in the water and the seahorses’ bloodstream to equalize on the way up.
At present, there is no consensus among the professional aquarists who use this method regarding the exact depth and length of immersion needed to effect a cure. I’ve encountered decompression times ranging from 2 days to 10 days and depths ranging from 10 feet in large aquaria (Paul Groves, pers. com.) to over 35 feet at the bottom of the ocean (Bill Stockly, pers. com.), all of which worked equally well. Interestingly, the shortest immersion time was used successfully at one of the shallowest depths (4 meters) and cured seahorses afflicted with all the different forms of GBS (Paul Groves, pers. com.).
While the exact treatment protocol that will produce the best results remains to be determined, everyone whom has tried the decompression cure agrees as to its remarkable effectiveness. It cures external GBS (subcutaneous emphysema, a.k.a. tail bubbles), chronic pouch emphysema (pouch bloat) and internal GBS equally well. In fact, as long as treatment is begun early enough, before the emboli have caused irreversible damage, decompression has a very high cure rate. It is safe, provides the affected seahorses with immediate relief, and works for all forms of GBS.
Of course, the home hobbyist lacks the resources to apply decompression at the sort of depths employed by the professionals. But I am discussing the recompression-decompression cure in some detail for two reasons. First of all, a number of hobbyists have managed to construct homemade decompression tanks and chambers, and other enterprising hobbyists may wish to follow their lead (Lisa Hovis, pers. com.). Homemade decompression devices range from simple tubes of water 6-12 inches in diameter and 4-12 feet tall capped at one end, designed merely to increase hydrostatic pressure, to pressurized wide-mouth bottles complete with pressure gauges and bleeder valves (Lisa Hovis, pers. com.). Secondly, I suspect that when enough data comes in we will find that a depth considerably less than 10 feet and relatively short immersion times will prove to be adequate to resolve most cases of GBS.
For example, while working with the Hawaiian seahorse (Hippocampus fisheri) at the Waikiki Aquarium, Karen Brittain found that all the specimens kept in smaller, shallower aquaria developed subcutaneous gas bubbles within a matter of months, whereas H. fisheri that were maintained in tanks at least 1 meter deep fared much better (Bull and Mitchell, 2002, p37). The Hawaiian seahorse remains pelagic all its life, typically being found at least a mile offshore in deep water, and Brittain speculates that H. fisheri needs to migrate to depths unachievable under normal aquarium conditions to maintain proper physiological balance (Bull and Mitchell, 2002, p37). I think she is absolutely correct. It seems likely that H. fisheri follows a daily vertical migration pattern, perhaps synchronized with the movements of plankton. Her findings suggest that tanks a minimum of 3 feet deep can provide a measure of protection against GBS, and custom-built aquaria of those dimensions are certainly within the realm of the home hobbyist.
This remains a fertile field for future research. It has been suggested that should there be an outbreak of GBS in one of your aquariums, transferring the seahorses to an aquarium at least 3 times as deep can decompress the patients and prevent a recurrence of such problems (Wooten and Waughman, 2004). This suggestion has a lot of merit. Even upgrading to a tank that’s twice as deep would be quite advantageous in terms of GBS prevention. Much work remains to be done to develop decompression guidelines for seahorses and to determine what sort of depth is needed to confer protection from GBS to different species. But when it comes to GBS, two things are certain: deeper tanks are healthier for seahorses and recompression can achieve remarkable recoveries.
In short, many times your best bet to cure internal GBS may be to try a moderate form of recompression to help your seahorse recover. What I have in mind is confining the affected seahorse in a flow-through enclosure at the bottom of a 50-gallon Rubbermaid enclosure 40 inches deep, or something similar, for a period of about 3 days. Once the seahorse is immersed at the bottom of this homemade "decompression chamber," you cannot raise it to the surface again for daily feedings. Since your decompression chamber will have no biofiltration, I would simply fast your seahorse while it recompresses at depth. It can easily go without eating for a few days and that will help eliminate any ammonia spikes in the meantime.
If you decide to try this, be sure to keep your makeshift decompression chamber well-aerated. A shallow airstone anchored just below the surface — NOT at the bottom of the decompression chamber! — to provide surface agitation and oxygenation should suffice.
When the recompression period is finished, raise the seahorse to the surface (or lower the water level in the hydrostatic chamber) gradually, in a series of stages, over a period of several hours, to assure that the patient decompresses completely and the gas emboli don’t reform.
Lighting your homemade decompression chamber isn’t really necessary. Seahorses have outstanding visual acuity and see very well under low light conditions (a couple of species are even said to have adopted nocturnal behavior in the face of heavy fishing pressure), so your female seahorse will be able to see well under the ambient light levels that penetrate and 50-gallon bucket. You won’t be feeding her while she’s undergoing the decompression cure, so she doesn’t need to be able to see well enough to hunt small prey or anything like that, and the darkened conditions may give her a sense of security and help her relax, since she won’t be feeling so exposed and vulnerable.
If you want to keep an eye on him periodically while he’s undergoing pressurization, you can just take a quick peek now and then using a flashlight.
When the recompression period is finished, raise the seahorse to the surface (or lower the water level in the hydrostatic chamber) gradually, in a series of stages, over a period of several hours, to assure that he decompresses completely and the gas emboli don’t reform.
One of our other Club members (also named Christine) has used this method to cure her seahorse of internal GBS after Diamox baths had been tried unsuccessfully. Here is how Chris described her experience with GBS, and her treatment method with her homemade decompression chamber, in posts to the group:
Hi — After 3 days of diamox Heidi was still buoyant (the diamox did not
seem to have helped at all), and swimming with the tip of her head
sticking out of the top of the water, clearly frustrated with her
situation. I looked at her with a magnifying class, and can’t see any
external signs of bubbles. I also don’t see any signs of bloating or
I followed Pete’s suggestions, took her off the diamox to restore her
appetite, gave her 1 day of rest in the hospital tank with clean water
and Kanamycin. She ate well yesterday and this morning. I rigged up
an inexpensive way of submersing her to 3 times the depth of my 30
gallon display tank. (I priced building a 6 ft deep tank out of an
acrylic tube attached to a base, or acrylic rectangles
attached to a base, and it came out to be anywhere from $250 to $400.
They wanted to charge $175 per linear foot of the acrylic tube thick
enough to safely support a 5 or 6 ft column of water). I’m going to
try the cheap method first, and will build a deeper aquarium if she
needs a greater water pressure.
So-I have her in a ‘critter keeper’ (small plastic container with a
lid that has slots in it and a viewing window in the center) with 2
soft rubber hitching posts. The lid has 4 large criss-crossed rubber
bands on it just in case the lid comes off. I made sure there weren’t
any bubbles underneath the critter keeper or underneath the little
clear viewing lid on the top. I bought a 50 gallon rubbermaid bucket
which gives a water depth of 3 1/2 ft when filled. The critter keeper
is inside a 5 gallon white bucket weighted down with a signature
coral, with a rope tied to the bucket handle (made it easy to lower
into the big bucket). I lowered her slowly this morning, and she
seems fine (not pinned against the lid of the critter keeper, and she
is able to go between the 2 hitching posts). I have an airstone going
at the surface of the deep bucket, as Pete suggested. I can see her
with a flashlight. Her breathing looks normal.
I filled the 50 gallon bucket yesterday with the shower! and let it
‘degas’ for one day (also to make sure that it didn’t spring a leak.
It is in the bathtub). The water temp is 70 degrees. I matched the
specific gravity and ph of the hospital tank.
Heidi is going to remain there for 2-3 days, as per Pete’s suggestion.
After that, I will bring her up very slowly (or unload the water from
the big bucket very slowly). I hope this works! Our big bathroom has
been completely taken over with buckets, hospital tank, salt mix, etc.
Wish us luck!
And here is Christine’s follow-up message after the recompression-decompression treatment was completed:
Hi Pete and Everybody, Heidi is okay! No more floating. I unloaded
the water from my makeshift compression chamber very slowly, as per
Pete’s suggestion, rather than pulled up the critter keeper from the
bottom (much safer to unload the water). I then transferred the
critter keeper she was in to a 5 gal bucket of clean saltwater,
and she swam out when I opened the lid. I decided to do a water
change in the main tank before putting her back in, and used the water
I pulled out of the main tank (74 degrees) to warm up the water she
had been in (70 degrees) to help re-acclimate her to the main tank.
She is eating and swimming as normal, back to her aggressive self with
the turkey baster and Mysis. She is very happy to be back in the
display tank, and is enjoying swimming all around, once again
neutrally buoyant. She was sooo happy to see her favorite coral
colored fake coral. Her color is going back from being dark brown
(her under stress color) to light brown/gold today. I hope to see
her go back to her coral color soon. Thanks for your help Pete!
I hope I never again have a SH with the floaties!
For the record, she was in a critter keeper inside a 5 gal bucket
weighted down with a fake (Signature) coral at the bottom of 40 inches
of water in a Rubbermaid 50 gallon bucket (on wheels-a new bucket). I
had an airstone at the top as per Pete’s instructions. She was in for
2 1/2 days.
For best results, the decompression sure is often combined with antibiotic therapy and treatment with Diamox. It is a simple matter to administer a regimen of antibiotics while the seahorse is submerged at the bottom of the 50-gallon Rubbermaid bucket. (Just don’t perform any water changes while the seahorse is undergoing recompression-decompression.) This would help prevent any secondary infections which are often associated with GBS or stress, and would also cover all the bases if you suspect the underlying cause of your seahorse’s positive buoyancy may be due to a bacterial infection.
For the antibiotic therapy, kanamycin, neomycin, and nifurpirinol are the antibiotics I prefer. I would recommend using two of them (i.e., kanamycin/neomycin or nifurpinol/neomycin) in combination for even greater efficacy, as described below, but if you can only obtain one of them, kanamyacin is the best choice in my opinion:
This is a potent broad-spectrum, gram+/gram- antibiotic. It is wonderfully effective for aquarium use because it is one of the few antibiotics that dissolves well in saltwater and that is readily absorbed through the skin of the fish. That makes it the treatment of choice for treating many bacterial infections in seahorses. Kanamycin can be combined safely with neomycin to further increase its efficacy. Like other gram-negative antibiotics, it will destroy your biofiltration and should be used in a hospital tank only.
Nifurpirinol is a nitrofuran antibiotic that is the active ingredient in many commercial preparations designed for use in the aquarium. It is stable in saltwater and rapidly absorbed by fish, making it the preferred treatment for fungal infections in seahorses (Burns, 2002). Nifurpirinol is photosensitive and may be inactivated in bright light, so use this medication only in a darkened hospital tank.
Nifurpirinol may be combined with neomycin (see below) to produce a potent broad-spectrum medication that’s effective against both fungus and bacteria. Nifurpirinol/neomycin is therefore a great combination to use when you’re not certain whether the infection you are treating is fungal or bacterial in nature.
Neomycin is a very potent gram-negative antibiotic. Most of infections that plague marine fish are gram-negative, so neomycin sulfate can be a wonder drug for seahorses (Burns, 2002). As mentioned above, it can even be combined with other medications such as kanamycin or nifurpirinol for increased efficacy. For example, kanamycin/neomycin is tremendous for treating bacterial infections, while nifurpirinol/neomycin makes a combination that packs a heckuva wallop for treating mixed bacterial/fungal infections or problems of unknown nature. Keep it on hand at all times.
Neomycin will destroy beneficial bacteria and disrupt your biological filtration, so be sure to administer the drug in a hospital tank.
One other thing to keep in mind is water temperature. Since you’re homemade decompression chamber is unheated, the water temperature will gradually fall over the three-day treatment period. This is fine and to be is expected — and even beneficial in many respects — but it does mean that once the decompression period is over, you may have to acclimate the seahorse for temperature before returning the patient to the main tank.
If you can obtain sufficient Diamox, you can also consider treating your bloated stallion with the acetazolamide, Tom, but it often works bests for subcutaneous emphysema and pouch emphysema, rather than internal GBS. Acetazolamide can either be administered orally by injecting a solution made from Diamox (the tablet form of acetazolamide) into feeder shrimp or the tablets can be used to administer acetazolamide as a series of baths instead.
If the seahorse is still eating, you can administer the acetazolamide orally, which will allow you to treat the affected seahorse in the main tank amidst familiar surroundings and in the company of its tankmates where it is the most comfortable. You get the acetazolamide into the food by preparing a solution of the medication, as described below, and then injecting it into live feeder shrimp or even the large Piscine Energetics frozen Mysis relicta. The medication is deactivated fairly quickly once you prepare the solution for injecting, so you must prepare a new acetazolamide solution each day during the treatment period. Here’s how to proceed:
Administering Diamox (i.e., acetazolamide) Orally
I have found that acetazolamide is often more effective when it’s ingested and administering the medication orally allows you to treat the seahorse in the main tank where he’s most comfortable and relaxed.
If you can obtain a small syringe with a fine needle, the acetazolamide solution can simply be injected into feeder shrimp or even frozen Mysis. Mic Payne (Seahorse Sanctuary) used this method of administering acetazolamide successfully when he had recurring problems with GBD due to maintaining a population of Hippocampus subelongatus in shallow tanks only 16-inches (40 cm) deep:
"Seahorses maintained in this system are susceptible to gas bubble disease. Specimens with bubbles around the eyes or under the epidermis of the tail are readily treated with acetazolamide (Diamox tablets 250 mg). Mix a very small amount of crushed tablet with water and inject it into several glass shrimp that are then frozen. These are then fed to the target animal at the rate of two per day for four days. Bubbles disappear on the second day."
Hawaiian volcano shrimp or red feeder shrimp (Halocaridina rubra) work great for this. If a fine enough needle is used, they will survive a short while after being injected — long enough for their twitching and leg movements to attract the interest of the seahorse and trigger a feeding response.
Leslie Leddo reports that a 1/2 cc insulin syringe with a 26-gauge needle was ideal for injecting frozen Mysis or live red feeder shrimp. They plump up when injected and ~1/2 cc is about the most of the solution they can hold. There bodies will actually swell slightly as they are slowly injected and excess solution may start to leak out. The 26-gauge needle is fine enough that it does not kill the feeder shrimp outright; they survive long enough for the kicking of their legs and twitching to assure that they will be eaten.
If your stallion is no longer eating, Tom, then you will need to administer the Diamox in the deep pressurization chamber and/or a hospital tank as a series of baths by crushing up the medication and adding it to the treatment tank instead (if you add the medication to the deep pressurization chamber, you can only add the initial dose, since obviously no water changes are possible while the seahorse is undergoing compression/decompression):
The recommended dosage is 250 mg of acetazolamide per 10 gallons with a 100% water change daily, after which the treatment tank is retreated with the sole light at the dosage indicated above (Dr. Martin Belli, pers. com.). Continue these daily treatments and water changes for up to 7-10 days for best results (Dr. Martin Belli, pers. com.).
The acetazolamide baths should be administered in a hospital ward or quarantine tank. Acetazolamide does not appear to adversely affect biofiltration or invertebrates, but it should not be used in the main tank because it could be harmful to inhibit the enzymatic activity of healthy seahorses.
Using the tablet form of acetazolamide (250 mg), crush the required amount to a very fine powder and dissolve it thoroughly in a cup or two of saltwater. There will usually be a slight residue that will not dissolve in saltwater at the normal alkaline pH (8.0-8.4) of seawater (Warland, 2002). That’s perfectly normal. Just add the solution to your hospital tank, minus the residue, of course, at the recommended dosage:
Place the affected seahorse in the treatment tank as soon as first dose of medication has been added. After 24 hours, perform a 100% water change in the hospital tank using premixed water that you’ve carefully aerated and adjusted to be same temperature, pH and salinity. Add a second dose of newly mixed acetazolamide at the same dosage and reintroduce the ailing seahorse to the treatment tank. After a further 24 hours, do another 100% water change and repeat the entire procedure until a total of up to 7-10 treatments have been given. About 24 hours after the final dose of acetazolamide has been added to the newly changed saltwater, the medication will have lost its effectiveness and the patient can be returned directly to the main seahorse tank to speed its recovery along.
One of the side affects of acetazolamide baths is loss of appetite. Try to keep the affected seahorse eating by plying it with its favorite live foods during and after treatment, until it has fully recovered.
The seahorse usually show improvement of the tail bubbles within three days. Dr. Martin Belli reports they nearly 100% success rate when this treatment regimen is followed for 7-10 days, and most cases clear up in less than a week. Expect to treat for the full 7-10 days when treating internal GBS with Diamox in a hospital tank, if it is to have any affect.
Okay, Tom, those are my thoughts on the matter. Pressurizing the seahorse at a depth of at least 40 inches is probably your best bet, and if you can treat the water in the homemade decompression chamber with antibiotics and Diamox at the same time, that will be even more helpful. But if the stallion is still eating, go and try administering the Diamox orally to him while he remains in the main tank, especially if you are able to perform a my last version and relieve his positive buoyancy.
Best of luck resolving this problem and restoring your stallion to good health, sir!