[hoppycalif]

Dechlorinators used to be pretty simple, incorporating one chemical that neutralizes chlorine in water. But, then the water companies began using chloramine instead of chlorine. Chloramine is a mix of ammonia and chlorine that lasts much longer in the water than just chlorine does. The old dechlorinators don't work for chloramine.

I suspect those cheap pond dechlorinators are the simple version, so I most certainly wouldn't trust one of them to be adequate in an aquarium. Seachem Prime isn't terribly expensive and the dosage needed is very small, so a bottle lasts a long time. That is a much better buy.