Here it is (first draft):
Algae is an important indicator for how many things we have done wrong.
Something is missing in the plant … not about what we give it but what the plant can actually take. Example, you have access to a trust fund, but you aren’t old enough to get the cash. You dose iron, but the plant can’t absorb it. You have nice sneakers, but no feet.
To correct algae: Basically every argument/plan of attack has this: adjust ferts, CO2, or light.
The goal is for everything to be running properly - decreasing light reduces O2 evolution and metabolism (which cleans up nasties from water column (especially if we get things running properly)), so it isn’t a smart option.
My choice is ferts or CO2 (always Flow should be optimized first). If your flow is bad and you cannot change it, then just change ferts, since you will likely be able to get away with less optimal flow to adapt to different ferts anyways.
On CO2, if it is already maxed (and flow is bang on): 1) you kill livestock 2) you drop pH too far affecting plant mechanism and/or bacteria.
Ferts also give you lots of O2 evolution (up to max growth), but when paired with low light, it is not healthy.
An EI system with rich substrate and highlight properly running is the healthiest system around. But it is hard to get the healthy plant forms under EI without driving the system hard. If something is lacking, then it gets less healthy.
Ok:
We have two different kinds of algaes (ones like plants and ones less like plants)
1) Ones like plants
In order of how “how off the mark you are" from least to greatest:
i) Green thread
To correct: Increase water column dosing a bit (at whatever concoction you are using). Or just leave it and hope the plants adapt and we trim away old, affected growth.
ii) Green Spot Algae
Less common on stems (access to soil) and more common on epiphytes (more sensitive to column dosing).
I have never seen it on stem plants that have access to soil … on inert, yes.
Go to ferts: Fix your column targets - increase or decrease GH, play with NO3/PO4 … K will only help when there is soil around (probably). Bring them as close to the boundaries as we set out here:
A reflection - putting it all into one scape
iii) Beard algae
Again, pretty rare on stems in rich soil.
Black beard algae turns green under higher light.
To correct: After CO2, fix your column targets.
2) Ones less like plants
These are protists like things so point to issues in microbial complexes and probably plants will show issues and other algaes shortly thereafter too.
What to bacteria things need?: O2 and pH. This is why we fix light at 100 - maximize O2 when everything else is on point.
i) Diatoms
More light and temp to speed up the maturation process. High light tanks from startup rarely see diatoms, if ever. If they do something else wrong, other algaes show up.
ii) Green Dust Algae
pH too low (waiting three weeks sometimes work … maybe because the plants grow in and use up the CO2). Ease off the CO2. If your CO2 is off, then you will get other algaes in response to this … then you need to look elsewhere and then perhaps that fix will increase CO2 consumption and then likely fix the pH issue.
iii) Cyano
Increase all column fert – just NO3 may skew the overall balance promoting other issues … but it may also bring the tank back to balance for a period of time until substrate runs out …
iv) Staghorn
Something seriously bad happened. There will be more algae to follow this one - a phase of establishment. Give it time to let it settle and see if anything else comes up. Start with light. Normally BBA follows if you don’t fix the root issue.