Here's some more info I found. Turns out that sulfur compounds, like those used in the aquarium water conditioners, are oxygen scavengers, which would not be good for hydro systems where aeration is important. Here's the
link. It's mostly about using vitamin C to dechlorinate, but it also summarized the other methods. Here's the part about the sulfur compounds.
Chemical Methods
Chemical methods of dechlorinating water are faster than passive methods. Water system operators may use sulfur compounds to dechlorinate water. However, to properly neutralize chlorinated water, operators need both caution and experience when using sulfur-based chemicals (Hill 2003). Sulfur-based chemicals are oxygen scavengers that will lower the dissolved oxygen in the receiving lake or stream, and some sulfur compounds are hazardous chemicals. At least two studies suggest that chlorinated and sulfonated water (sulfur-based dechlorination) poses a hazard to some sensitive aquatic species (Hall and others 1982; Rein and others 1992).
It also says you can use sodium ascorbate instead of ascorbic acid. That would avoid pH drop, though calcium ascorbate would be better for plants and is also available. You would still have fluoride in the tap water though, not sure how bad that would be for plants. For that you really would need a deionizer or RO.