The Praziquantel is safe for all animals and fish and is actually used to treat tapeworm in cats and dogs. But it also works well when treating fish for tapeworm.
Levamisole is also safe for fish and is made to treat livestock (sheep, cattle, chickens, etc) for some types of intestinal worms. I have used Praziquantel and Levamisole on all types of adult and juvenile fishes with no problems. Neither of these deworming products will affect plants or filter bacteria.
Most fish carry intestinal worms and it is a good place to start when fish do a stringy white poop and the fish is still feeding.
The only way a fish vet can tell what the fish is carrying internally is to either kill the fish and have a look inside, or take a sample of poop and put it under a microscope to check for bacteria, protozoa or worm eggs. Fish can have all of these at the same time and as long as the fish is in good condition there is not normally any issues. But if water quality deteriorates or the fish gets stressed from something, then any of these internal problems can cause the fish to go downhill very quickly.
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If you have ammonia in the aquarium water, the fish and frogs will be stressed from that. Ammonia should be broken down by beneficial filter bacteria and if it isn't, then there is a problem with the filter.
What sort of filter do you have?
How often do you clean the filter, and how do you clean the filter?
Filters should be cleaned at least once a month and filter materials should be washed in a bucket of tank water.
If you have carbon (black granulated substance) in the filter, that can be removed and replaced with a filter sponge.
If you have an ammonia absorbing granule (white chalky gravel) in the filter, that should be removed because it interferes with the filter bacteria development.
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If you have chloramine in your water supply, then a dechlorinator will break the ammonia/ chlorine bond and remove the chlorine, but it will leave small amounts of ammonia behind. Some water conditioners will also bind to this ammonia and make it harmless while the filters break it down into nitrite and then nitrate.
If you are using well water and it has ammonia in, you can put the water into a large plastic container and put a filter with an ammonia absorbing granule in, and let the filter run on the container of water until all the ammonia in the water has been removed. When there is no ammonia left you use the water to do water changes on the tank. "Wardley's Ammogon" is one brand of ammonia absorbing granule but there are other brands too including "Zeolite".
You can also run a carbon filter on the container of water to remove any chemicals or heavy metals that might be in it.
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Frogs are very sensitive to ammonia and other chemicals in water and are best kept in their own tanks without fish. They also need very good filtration to remove any ammonia that is produced.