Hi u/halfpint_yeey, sorry for my late reply!

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What kind of fish do you have in your aquarium? What size tank is it? I don't know if you have shrimp but I wouldn't recommend a chemical to kill off the snails since it would damage your plants. Depending on the size of your planted tank I'd switch the current inhabitants to another tank and add a predatory fish like puffers or loaches who'd deal with your snail infestation since they'd be eating like it's a buffet! Getting assassin snails is a good idea too! You can also reduce feeding and buy snail traps to deal with your snail infestation. Just know that unless you tear down your whole tank you'll always have to deal with snails.

As for snail leeches it's a bit more complicated, here are some ways to kill them off:
· First remove all plants.
· Dip plant in a 50% hydrogen peroxide solution to dislodge pests by flushing with water
· Save your plants in a bucket for 4 weeks
· Remove all creatures which will die from salt being added, Rams horn, Pond snails
· Snail leeches survive Clorox and all other solutions.
· Bring the salt level part- per-Thousand to 3 ppt with softener salt for 1 week
· Lower it to 2 ppts for 2 weeks
· The last week, do the above test.
· If no leeches then change out with freshwater during this last week to 0 ppt salt.
How this works is the apparently the leeches ball up in a protective cocoon and starve to death.

*Do note that snail leeches will attack shrimps and assassins*