One thing that is rarely discussed when algae or CO2 and plants are brought up:
How long does it take for the plants to get growing really really well after being subject to neglect?
It can be all of these.
It depends on the intensity of the neglect, how much effort to put into rectifying things etc.
So do not assume a dosing routine is bad, good etc, without going to distance, and also using a good control tank.
If you stop adding PO4, what will that do?
Will it increase of decrease CO2 uptake?
Decrease, because the plants are no longer limited by CO2, they are now limited by PO4!
So limiting CO2 is really the issue, not excess PO4.
And that's why you have/get algae, not PO4 or non specific tank "balances" etc.
You create limitations for plant growth and provide good cues for algae to germinate(CO2 variations, NH4 build up, organic detritus dirty filter).
You can use these limitations to your advantage to some degree, but it's highly variable, which is why we have so many folks claiming all sorts of muckery about algae.
You must have a well running stable tank and add the treatment of interest to "test" anything with respect to growth, algae blooms etc. If you cannot or are unwilling to do that, your test has no power to conclude a dang thing.
It seems that a longer time frame is needed to get rid of and control some species of algae. That makes sense.
Do you want to beat it back very aggressively?
Or hit it softer and wait a few weeks?
Which method is easier on the plants?
Do you just work on the algae once and then wait, or keep up some treatment over time?
Good long term maintenance habit are what allows folks to have nice tanks over time.
Good CO2 is not the easiest thing to do, but rather than using PO4 to limit plants, try less light.
Here's a tank with 1.5 watts a gallon using T5 lights:
Less light= less cost to you and the electric bill, cooler temps, less junk in the way, more manageable growth rates, and of course, like PO4..................less light= less CO2 demand by the plants.
So it's much easier to balance and wiser/cheaper, easier, no testing involved than using PO4 to control CO2 demand.
It's basic plant growth physiology, but I still get folks that want to argue that point.
Light drives CO2 uptake which drives N and P uptake.
More light= things will crash much much harder if you mess something up(and you will at some point) than at lower/less light.
If you limit CO2 and provide stable low CO2, such that the plants adapt to the low CO2, they will grow slow and need only low light, so that light is low, CO2 is slow, what do you think they requirements are for NO3 and K+, and PO4 are in such tanks?
About 10-20x less than a higher light CO2 enriched tank.
What about the requirements for water column dosing if you louse that up and have good sediment sources such as ADA As?