It's probably fine, I've used pond dechlor on a few occasions since it's more readily available around here.
An even cheaper alternative is to get some sodium thiosulfate crystals and make your own dechlorinator, one lb of the stuff mixes into 1 gallon of water and is dosed at 1 drop per gallon of tank water, so it can dechlor 30000 gal+ per bottle.
1lb of sodium thiosulfate crystals is around $3.25 at angelsplus.com, I'm sure there's plenty of other places that carry it as well.
The only downside is that it does nothing to detox heavy metals, or temporarily bind nitrogenous wastes (like Prime, for example), if that is even an issue with the water to begin with.