Fish with tapeworm or other intestinal worms (round/ thread) don't hang out by the surface.
Intestinal worms normally cause the fish to lose weight over time even tho the fish are eating well. In severe cases, fish that are heavily infested with intestinal worms can actually become fat and look pregnant. This is due to the massive number of worms in their digestive tract. After deworming these fish look really skinny but regain weight within a month or so of the treatment.
Praziquantel is used to treat tapeworm and gill flukes.
Levamisole is used to treat thread/ round worms that affect fish.
API General Cure contains Praziquantel and Metronidazole.
Metronidazole (Flagyl) is a medication normally used to treat internal bacterial or protozoan infections in people and might have wiped out your beneficial filter bacteria. You should check ammonia and nitrite levels whenever using this product, or whenever you get a sick fish.
Whenever you treat fish for intestinal worms (tapeworm or thread/ round worms) or gill flukes, you should treat once a week for 3 weeks. The 3 week program kills any baby worms or flukes that hatch from eggs in the tank or in the fish. If the water is cool, (eg: you are treating goldfish), continue treating once a week for 4 weeks. Do a 75% water change and gravel clean the substrate 24-48 hours after treatment.
Praziquantel and Levamisole are both safe for all fish (including scaleless fishes), plants and filter bacteria, and can be used in fresh, brackish or salt water aquariums. You can mix them with food or just add the chemical to the tank and it dissolves in water. I usually do both, feed and add it to the tank.
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Gill flukes will cause fish to become pale due to the blood they suck out of the fish. The gill flukes damage the gills and reduce the surface area of the gills that are exposed to the water, making it harder for the fish to breath. Infected fish might hang around the surface or near a filter outlet to get more oxygen.
Praziquantel is the safest medication for gill flukes. The most common medication previously used was Trichlorphon (aka Dipterex) and is highly toxic to fish, birds and other animals and doesn't work well anymore due to excessive misuse over the last 40 years.
Salt can also be used to treat gill flukes. Use 2 heaped tablespoons or rock salt, sea salt or swimming pool salt per 20 litres. Keep the salt levels like this for at least 2 weeks and it should fix the problem. However, Praziquantel treats tapeworm too so is worth using on any new fish before they are added to a display tank.
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Red gills are usually caused by poor water quality or something toxic in the water. Check the water quality and do a 75% water change and gravel clean the substrate each day for a week. Clean the filter if it hasn't been done in the last 2 weeks. Increase aeration/ surface turbulence.
Fish going pale and gasping at the surface can be gill flukes, a fungal or bacterial infection on the gills or an internal bacterial/ protozoan infection.
Internal infections normally cause the fish to stop eating.
Bacterial and fungal infections on the gills are rare but do occur. The fish normally stop eating and die within a few days of this developing.
Gill flukes are the most common issue and the fish will continue to eat but lose condition and eventually suffocate.
Guppies also have issues in soft water with a GH below 200ppm and a pH below 7.0. And they are prone to external protozoan infections if the tank isn't kept clean.
