Thank you for waiting. I 'm very sorry to have to give you bad news, but I feel you deserve honesty. Unfortunately, when a fish's spine bends like this, even somewhat, it is very serious. There are three main causes of this condition in mature fish. One is a spinal injury. Another disease that can cause the spine to bend is Myxosoma cerebralis. It causes the bent spine and often, but not always, the fish will start whirling in a circle, so it is sometimes referred to as whirling disease. Even when a fish doesn't whirl, it usually floats in a vertical position.
Finally there is fish tuberculosis. The main symptoms are spinal deformity, weight loss, and skin problems including scale loss, color changes, and skin lesions. Not all fish will develop all the symptoms. I think it is more likely that Buster has whirling disease, but the treatment is the same for both diseases. Until recently, there was absolutely no treatment for either whirling disease or fish tuberculosis, but sometimes now good results can be obtained with kanamycin. Many fish keepers simply choose to euthanize a fish that is infected because treatment has to be carried out for an extended time, usually about 3 months. Not all fish respond to it, but since Buster is special to you, it is probably worth trying. Both diseases are slightly contagious to other fish, but often they don't become infected unless stressed in some way. Here is an online source of a smaller amount of kanamycin:http://www.americanaquariumproducts.com/Seachem.html#kanaplex
You'll see on that page that it can be combined with Furan 2 and Metronidazole for stubborn bacterial infections. Both fish tuberculosis and whirling disease are stubborn, so you may want to consider this. Just follow the instructions on the medication labels. No other antibiotics have any effect on these diseases. If you choose not to treat, Buster will possibly live for quite some time, but his condition will steadily worsen.
I also want to give you some information about water quality because what you see on the testing kits isn't reliable for goldfish. Nitrates are one of the end stages in the nitrogen cycle, and under normal conditions, they don't cause problems. The numbers you are obtaining are not anything to worry about. You can read more about nitrates here:
Ammonia at .25 ppm is another story. That isn't enough to be fatal, but levels that high weaken the immune system, and that makes fish susceptible to other diseases. Despite what the test kit may say, there is no safe amount of ammonia for goldfish. Both ammonia and nitrites must be at zero. If you still have ammonia in your main tank, you can start a series of water changes. Begin by changing 1/3 of the water in the tank. Be sure the new water is the same temperature as what's in the tank already, and that it has been dechlorinated.
If you have filters that use activated carbon, put in new carbon or cartridges. Then test your water every day. Every day after today, until ammonia and nitrites are at zero, you'll need to change 10-20% of the water, always temperature-matched, dechlorinated water.
I'll also give you a few bits of information on hole in head disease in case any other fish develop it. It's believed that several factors interact in causing the disease - a parasite, less than optimal water conditions, and a sub-par diet. Treatment involves fixing all of these problems. Metronidazole is the only medication that kills the parasite. I already explained what to do about water. Make sure the food you're using is a high quality one, such as Mazuri.
If you have more questions, let me know by clicking on REPLY. I hope Buster respond to medication.
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