I was going to say, L. aromatica grows to be a large plant, I wouldn't recommend it to a 25L tank. But if you are going to let it emerge, it could be manageable.
Do you ask this because the tank is covered? If so, better not to have aromatica, in my opinion. If it isn't covered, then just fill it up normally and let the plant break the surface when it gets there.
As for your concern regarding chemicals in the plants hurting the snails, to me that is completely unheard of. I see people quarantining plants to prevent the accidental introduction of snails, or maybe some pathogens, but have never seen it because of a concern over chemicals.