Hole in the head disease in fish is caused by a dirty environment. It can be a dirty filter or dirty substrate, or both (usually both). The best treatment is big (75-90%) daily water changes and gravel cleaning. If there is no improvement after a couple of weeks of daily water changes and gravel cleaning, then you look at medications.
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Erythromycin is an anti-biotic and should only be used to treat known bacterial infections that have not responded to normal fish medications. Improper use or mis-use of anti-biotics causes drug resistant bacteria that kill people, animals, birds, reptiles and fish.
Herbtana and garlic won't do anything to help this.
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The fish is starving to death and needs to be fed 3-5 times a day for at least the next month. Use a basic tropical flake and then add some frozen (but defrosted) foods like brineshrimp, marine mix (contains prawn, fish & squid), bloodworms, raw or cooked prawn without the shell. Mysis shrimp is good if they eat it.
Live adult brineshrimp (available from most pet shops) can also be used.
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The medications I mentioned are to deworm the fish and are completely safe for any and all fresh, salt and brackish water fishes. They are perfectly safe for baby fish, loaches, catfish, angels, tetras, livebearers, etc, as long as you don't overdose.
Deworming medications will not harm plants or filter bacteria. And they never affected any of my snails.
Intestinal Worms like tapeworm and threadworms cause the fish to lose weight, continue eating and swimming normally, do a stringy white poop. Fish can do this for months and not be too badly affected. In some cases, fish with bad worm infestation will actually gain weight and get fat and look like a pregnant guppy. This is due to the huge number of worms inside the fish.
You can use Praziquantel to treat tapeworm and gill flukes. And Levamisole to treat thread/ round worms. If you can't find these medications, look for Flubendazole.
Remove carbon from filters before treatment and increase aeration/ surface turbulence to maximise oxygen levels in the water.
You treat the fish once a week for 4 weeks. The first treatment will kill any worms in the fish. The second, third and forth treatments kill any baby worms that hatch from eggs inside the fish's digestive tract.
Treat every fish tank in the house at the same time.
You do a 75% water change and complete gravel clean 24-48 hours after treatment. Clean the filter 24 hours after treatment too.
Do not use the 2 medications together. If you want to treat both medications in a short space of time, use Praziquantel on day one. Do a 75% water change and gravel clean the substrate on day 2 & 3. Treat the tank with Levamisole on day 4 and do a 75% water change and gravel clean on day 5, 6 & 7 and then start with Praziquantel again on day 8.
The water changes will remove most of the medication so you don't overdose the fish the next time you treat them. The gravel cleaning will suck out any worms and eggs that have been expelled by the fish. Repeating the treatment for 3-4 doses at weekly intervals will kill any worms that hatch from eggs. At the end of the treatment you will have healthier fish.
