That's not correct. A healthy snail population actually reduces the risk of ammonia peaks, since they eat leftover food and cadavers. It's when all the snails die at once (e.g. treatment with algizide or snail killer). That's when you may get problems with ammonia. Or if you have a tennis-ball sized apple snail and it kicks the bucket.
In general, snails are our friends

They only become a pest when you feed too much.
HarleyK
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