Try this: deep vacuum the gravel there, replant etc.
You need to get the plants growing well, they will knock the algae back once you.
Clean filter etc often.
You can also do more water changes if you want and dose there after.
Good cO2 will help, plants will produce more O2.
Poorly growing plants that are slowed, in a lull etc, tend to be more likely to have algae issues.
PO4 should help if the CO2, NO3, trace dosing is good etc.
Blackout means a 2 layer black trash bag etc and no other light for 3 days, this is virtually 100% effective in killing what is there.
It does not by itself in any way prevent reinfestation.
Good trimming, good, CO2, PO4 etc, everything that makes plants grow well will prevent all algae from entering in. The focus is much more about the plant's needs, rather than worrying about the algae.
You do that, algae is much less an issue.
Another thing you can use that's much less harmful for algae is seaChem's Excel.
This at least grows plants(Not Vals, Hydrill, Egeria, liverworts- non stomata bearing aquatics-other than vals).
and is very mild to fish and shrimps etc.
Do daily water changes(50-70%) and full excel dose and a balckout for 3 days for any species of algae, this is a very effective method when combined with good dosing and maintenace thereafter.
It's also very selective and does no harm to the plants/critters.
Regards,
Tom Barr