Rick wrote:

it is likely that your weekly 30% water changes reduce your nitrate below
measurable levels. I do weekly 50% water changes in my heavily planted 77g
tank and dry dose ferts twice a week including a 1/2 tsp of KN03 (nitrate)
and I still don't measure much nitrate. Your plants will also be using up
nitrate. I wouldn't worry about it, seems everything is running o.k for you.
As far as daily 50% water changes are concerned you could do that if you had
the time but why bother.

Thanks for the info :-) I had read that there should be some nitrate in
the water, so I was a bit concerned that there isn't any nitrate in my
tanks. But if it doesn't matter then I won't worry about it.
I don't plan on doing daily 50% water changes. I was just wondering if
that was possible. I thought it was. I'll stick to my once or twice per
week water changes.
Thanks
Karen