Samuel,
regarding your step 5, you should increase CO2 instead. Nevertheless, I had a similar algae outbreak like yours before. My US fissidens, japanese hairgrass and crypt. parva are infested as what you described-"black & clustered". Here's what I done:
1) I bleach the equipments(i.e CO2 diffusor) infested with algae
2) Introduced a young SAE(total length around 2 inches long)
3) Clean my filter and increase CO2 rate.
Within two days, my hair algae are all cleared and nowhere to be seen. The SAE is capable of removing hair algae from my fissidens neatly[

]. I let the SAE remains in the main tank for an additional week and ensure all my plants are growing well before removing it. Yamato shrimps somehow are less interested in the hair algae than SAE.
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