Hi Missann!
I've been raising...even breeding...fish (cichlid family) for years. And, I agree that colored aquarium gravels should be perfectly fine for your orchids. Fish are extremely sensitive to toxins in the water (even sprayed around the tank) and if there was a leeching problem w/those dyes...many fish would die.
As for the dechlorinator...I would avoid using it in my orchid water. One of the main reasons is because many of them should not be used and/or should be used in very sparingly amounts in "planted" tanks. I'm not a chemist so I'm not real clear on the "hows" of this but...it's got something to do with the high levels of phospates in the products (used to buffer the water) -- apparently it locks up CO2 and makes it unavailable for plants. Now...I'm not sure how much that would affect orchids from a root standpoint but I personally wouldn't want to take the chance. The other reason is because the conditioners contain a lot of different chemical ingredients...phosphates, sodium based ingredients, buffers, etc, etc,....all things great for a fish and it's environment but of no real value to an orchid. Quite possibly harmful to the orchid.
If you're concerned about the 'stuff' that's in your tap water...I would recommend using distilled water...there's zero risk to the plants (they like it better than tap water anyway) AND it's a
heck of a lot cheaper than aquarium water conditioners.
Hope this help.
