I got the gift of a water garden last year for my 50th birthday and I am having a great deal of fun with it. The designer told me that the best way to keep the pond clear of string pond weed was to have a gravel filter. Well, the filter has been helpful, but I read that all water gardens will eventually suffer from pond weed until the garden stabilizes, and that is indeed the case with mine. I did not like the look of green water (pond weed plus the bottom green scum) and I did not enjoy seeing the liner when I looked into the pond (see the first photo). So I bought pond dye, called Deep Water in black, and added it half strength (I wanted to see what it would do before I added it full strength)(middle two photos). Deep Water is a vegetable-based dye that is advertised as being harmless to wildlife, pets, etc. I think the black dye is nicer looking than the blue, which looks more artificial to me. I do like the fact that the dye obscures the liner (last photo), but I am still undecided. I noticed that it has already faded somewhat, only 10 days after adding it. It will fade over time, so if I decide I don't like it, I just need to wait.
Happy Gardening!