I have decided that I reported erroneously in the OP on the green color on the fiberglass. I don't think that was the dye. I think it was an algae I had not noticed before.

I have now change out 60% of the water on two consecutive days and have decided the ''black'' dye is really a deep purple, not deep green.

I use black dye in my greenhouse pond and it does not hurt the plants. I've been using it for years. The greenhouse is hot and otherwise it stays green. I keep it really black and yes, it takes a very small amount of dye to do this. I have had the same bottle for probably five years.

i use a blue dye for ponds with no problems. i take a small amount in a small container and add it in slowly in the waterfall.i do not put it all in at once, but watch and wait to see the results. it does not take long to get the desired results.

I might be interested in using some pond dye. My water is clear but because of the algae on the liner it always has more of a green look since you are looking through the water at the green algae. Black and blue look interesting but I don't want an artifical look. So I am a little scared to try it.

QUOTE: I don't want an artifical look

The algae on the liner is the 'natural' look...a sign of a healthy pond. I'd be worried if it wasn't visible.

blessings,
~digger