It's the end of the week, and I suddenly noticed a bit of hair algae on some of the leaves. Just the tiniest bit, but enough to catch my attention.
I knew something was wrong because "healthy plants don't grow algae" and all that jazz. I tested the water for
NO3 and
PO4, and found that I bottomed-out of NO3 and still had some PO4 left. Which is pretty shocking since I'm dosing 30ppm NO3 in one 20ppm recovery dose, and one 10ppm midweek dose. That means that this tank is consuming more than 4ppm NO3 per day.
I DO have the lights set to ~80% (which is a lot for this shallow tank) and the heater is set to 74F, both of which are driving plant metabolism upwards.
However, plant health seems to suffer after a water change, and by the end of the week. Things are fine, but not exceptionally healthy. As I was playing around with my nutrient calculator, I realized why:
With my current setup, a tank consuming 4ppm NO3 per day with a weekly total of 30ppm dosed the way I do, has
swings of over 14ppm between water changes:

14ppm swings of NO3 isn't the end of the world, but it's not good.
For reference, here's the same scenario but at 2.5ppm NO3 consumed per day, like where the tank likely was a month ago:

Much more stable.
Now I realize that
determining stable dosing really is, primarily, dependent on daily uptake. That's why I love this accumulation calculator I made, to learn about these things!
I've purchased a Hanna Nitrate Checker, and I
plan to do the marine-to-freshwater conversions to get a more accurate reading, so I can measure at 10am on Day 1 and 10am on day 2, and learn how much NO3 my tank is consuming. I'll probably do tests through the week to learn about consumption levels.
Examples of ways to keep levels stable (inlcuding a large weekly WC):
If you have a tank with only
~1.0ppm NO3 uptake per day, you could just front-load 15ppm per week and be good:

This would work for many low/medium energy tanks, or newly planted high-energy tanks that don't have a lot of mature plant biomass yet.
If the same tank starts consuming
~2.5ppm NO3 per day, you could start adding a midweek 10ppm dose for similar levels:

These levels are pretty common for daily NO3 consumption in many "high energy" planted tanks, especially tanks that have fast growing stem plants that put on a ton of biomass very quickly.
Finally, if your tank is going
bananas and consuming
>4ppm NO3 per day, you could increase both your initial dose and midweek dose to try to keep levels similar,
though the weekly max difference will always begin increasing mathematically, which isn't awful, but isn't great:

The max difference is 12ppm, which again, isn't the
worst, but plants will definitely be playing "chase" changing their internal enzyme structures to try to match the nutrient levels, which days days/weeks to get stable.
One way that I speculate keeping levels stable in SUPER HIGH daily consumption tanks (4-5ppm NO3, which is probably only common in heavily planted, high-light, high-CO2 dutch style tanks)
is via an initial dose after water change, then daily dosing as close to daily consumption as you can get.
In a tank that consumes ~2.0ppm NO3/day:

Yeah, that would be pretty stable, despite 70% weekly WC! That's thanks to the 10ppm "initial" dose.
What about the same tank, consuming 4ppm per day, but only dosing 3.5ppm per day?:

Again, only a max difference of 3ppm? That's
incredibly stable. The initial 10ppm dose basically just determines the average
ppm levels in the water.
I think I might give something like this a try; create a macro solution of known NO3 and PO4 (and
K) concentration, that is dosed in a large recovery dose after WC, but dosed daily via auto-doser as close to daily consumption levels can be.
I can accurately test daily consumption levels with the Hanna NO3 checker.
We'll see!