Good question but I don't really know. I'd imagine you could test on a set schedule and see how it changes over time?When everything is set up, do you have any way to get a ballpark guess of how many ppm of NO3 the plants eat? Always one of my biggest interests in a planted tank thread.
Got a decent amount of plants in the 75 but the 29 is the first "dedicated" planted tank that I've tried, so i'm sure there will be lots of ups and downs. I still picked relatively easy undemanding plants