Bad test kit or tank not fully cycled...since you’re using API it’s very possible it’s giving a false positive. If you can, get another test kit or take a sample to a lfs that uses some other kit.
For snails you can attach some nori with a rubber band to a pice of rock. Generally best to do at night when the fish are asleep.
For snails you can attach some nori with a rubber band to a pice of rock. Generally best to do at night when the fish are asleep.