Misleading Nitrate Test??

[cloud]

Thanks Oriongirl. There's plenty of it in my LFS, but I'm afraid to put it in my tank for a while yet as It's quite heavily planted and as you say it blocks light. My lighting's not too strong at the moment. I've got it at a level where the plants like it but don't bloom out of control. I'll probably have to invest in another bulb if they get much larger and propogate more, but for now It's at just the right level, so if I started blocking it off with duckweed I think I'd be in trouble.
But good advice for the future. A natural nitrate levels indicator such as that appeals to me.

 

[RTR]

...--duckweed is fantastic at removing nitrates ...--when I start seeing lots of duckweed, it means the tank is due for a larger than normal water change.

Me, too! But it also serves double duty - if the few duckweed I allow to remain are not multiplying, then I know that I need more ferts. It serves as an indicator at either end of the scale.