100-200ppm of KH is fine for livebearers. The high KH simply means your pH won't drop suddenly.
Aquarium water is full of different types of bacteria and fish ingest them all the time. If a fish gets run down from stress or poor water quality, they are more likely to develop dropsy or other internal and external infections.
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Is TB common? I had thought that a couple of my platys had it but I read that it's very unlikely. Also, is it transmittable to humans?
Any fish can be infected with Mycobacterium (Tuberculosis or TB). Australian and New Guinea Rainbowfish are regularly infected and livebearers and dwarf gouramis from Asia are too.
In 2006 I had TB in my tanks and did some research on the subject. Every pet shop and fish importer that I contacted, admitted they had, or suspected they had fish TB in their tanks on at least one occasion. I contacted most of the shops and importers in Australia. Most of the fish coming into Australia come from Asian fish farms and these farms also supply freshwater tropical fishes to most of the world. So if it's in Australia, it's highly likely it is in every country around the world.
Fish TB is also found in a lot of waterways and in Western Australia, the state government had trout farms where they bred and grew trout to be released into natural waterways for recreational fishermen. The main trout farm was in Pemberton in the south-west of WA and it had TB in its system. Basically the state government was releasing an introduced species of fish (trout) that were contaminated with TB into rivers so fishermen could catch them. Subsequently most of the fresh water creeks and rivers in the southern half of the state now have fish TB in them. The trout also eat the native fishes.
Australian native fishes never evolved with fish TB and were never exposed to it until 30 or 40 years ago and they have no resistance to it. This is why it's so commonly seen in rainbowfish. Other fishes from Asia have been exposed to it for thousands of years and appear to have some resistance to it.
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Fish can be infected with TB for months or even years before they show any signs. The most common symptoms include: the fish swelling up overnight, breathes heavily (usually at the surface or near a filter outlet), stops eating, does a stringy white poop, dies within 24 hours of showing these symptoms.
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Fish Mycobacteria (TB) is a very slow growing bacteria. Most common bacteria can double every few hours. Mycobacteria takes days or weeks to double.
In cold water, TB grows slower and goldfish can carry the bacteria for years before it affects them. In warm water, the bacteria grows quicker, but it's still a slow growing disease.
If fish are big, it takes longer for the bacteria to build up in numbers and kill the fish. A small fish has smaller organs and less bacteria are needed to damage it.
The bacteria kill the fish by destroying internal organs and causing organ failure. Basically a fish becomes infected by eating TB contaminated food or ingesting the bacteria with contaminated water. The bacteria settle into an organ somewhere in the fish's body and start growing. They grow slowly and build up over time. Eventually the bacteria damage the organ they are growing in and the fish swells up and dies.
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You can't treat fish TB because Mycobacterium cells are covered in a waxy coating, which prevents chemicals harming the bacterium and also protects it from the elements. The bacterium can remain dormant in shady areas or mud for many years. A fish health scientist I contacted about this in 2006, told me he found live but dormant fish TB in a dry river bed down south. The river had not had any water for 7 years, yet they still found live bacteria there. Hot and dry conditions kill the bacteria quicker. It dies in a couple of seconds at 60 degrees Celcius.
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People can catch fish TB, however people with a healthy immune system are less likely to develop a fish TB infection. People catch fish TB when open wounds in their skin are infected with TB contaminated water. If you wash your hands and arms with warm soapy water after working in a tank, you are less likely to contract the disease. If you have cuts, scratches, sores or any open wounds on your skin, avoid getting fish tank water on them. Wear a pr of rubber gloves or just stay out of the tank until the wounds have healed.
People with a weakened immune system (heart disease, lung problems, diabetes, cancer, HIV, old people, babies, etc), are more likely to develop localised TB infections.
If you develop any sores on your hands or arms that don't heal up normally or quickly (within 2 weeks), see your doctor and inform them that you keep aquarium fish. The doctor will probably try to put you on anti-biotics, however this is not good. Ask the doctor to take a swab of the sore and send it off for testing to see what is growing in the wound. The lab should culture the swab and test various treatments on it to find out which medication will work best. The results will be sent to the doctor, along with a list of medications that treat the disease. The doctor will then find a medication that is safe and suitable for you.
Do not take anti-biotics for a small sore that hasn't healed until it has been swabbed and identified in a lab. Then take the anti-biotic that works best on that specific bacteria.
People have gone to the doctor with small sores and been put on anti-biotics before a swab was taken. The anti-biotics don't work and the bacterium simply becomes resistant to that sort of anti-biotic. Because the anti-biotics don't work, the doctor prescribes another type of anti-biotic and this continues for months with no improvement. Eventually the doctor will take a swab and send it off for culture, but that can be 6 months later and by then you have big sores on your skin that are gross and can potentially contaminate other people with open wounds.
So just make sure you tell the doctor you keep fish and want any sores swabbed and sent off for culturing before you take anti-biotics.
Before you go to the doctors, or while you're waiting for the results, you can try using raw honey. You wash the wound with warm soapy water, dry it with a tissue, then rub raw honey into the wound. Put a bandaid over the wound to stop the honey going everywhere. Remove the bandaid and wash the wound and re-apply honey 2 times a day. Raw honey has chemicals in it that kill viruses, fungus, and bacteria and might help with fish TB. You normally see results after 3-4 days of applying honey and you continue using it until the wounds have healed over.
