Thank you all for your responses!
I should say that I have left out some of the details to avoid making my question unnecessarily complicated. We do have a medium-strength light, we are dosing several other nutrients in addition to the N (P, K, Flourish Comprehensive) as well as Excel. Through trial and error and some basic calculation I think we've been able to keep the dosing in balance. As roadmaster said, "I like to think I can tell what the plants are calling for...". In general we try to keep things low-tech.
The basic outline of our N dosing for the last 3+ months:
- After our water change, NO3 readings have been 5ppm.
- We are dosing 5ml of Seachem Nitrogen 2x a week:
---- per Seachem - Flourish Nitrogen
I calculate with 40gal of water in our 46 gal tank, that each 5ml dose would raise N at the equivalent amount that 2ppm(mg/L) of NO3 would.
- After 2 weeks (4 doses), before our 50% PWC, we would have added 8ppm NO3 equivalent.
- Before our PWC we measure 10ppm NO3, leaving me to assume that the plants have used approximately 3ppm (5 + 8 = 13... but 10 measured).
So the real question comes down to "How can I maximize the N available to plants while also minimizing the NO3 levels for the fish?"
Because I can only measure the NO3 levels (and perhaps not so accurately) I guess the best I can do is dose the Seachem Nitrogen and aim for a target level of NO3. I think it's safe to assume the amount of total N available to plants will be greater than the NO3 level (perhaps it's 2x) but as long as NO3 is at a safe level for fish, the actual level of total N is not so important... right?
If our NO3 is measured at 5ppm after a water change, and increases over 2 weeks to 10ppm, is that optimal for plants or should I aim for a higher target? I actually doubled my Seachem N dose this week, and I'll know in 2 weeks what the NO3 level comes out to at the end of our water change cycle.
Will the plants do any better with NO3 readings of 10-20 as opposed to the current readings of 5-10, or is this just overkill?
Thanks so much.