Hi, let me see what hypotheses I can think of:
-Maybe the fact that you only use plants with a lower metabolism and put too much ferts give the algae a chance to establish itself. Try adding fast growers, changing the water more, and dosing less ferts.
-Also try to shorten you photoperiod to up to 6-7 hours to see if that helps.
-Maybe the crushed coral has raised hardness so much that it bothers the plants but not the algae
-If this tank is new it could be that you started dosing too early, and the plants didn't have time to adapt themselves, and didn't consume too much nutrients. add that already nutrient-rich water with the aquasoil leaching nutrients and ammonia in the water, plus high light and you get an algae explosion. If your plants are new then they would need to adapt first.
-Dispose of any dying plant matter, it will only make things worse.
-I know a lot of members here start planted tanks and even very minimalistic iwagumis or slow-growth scapes (ferns, anubias and mosses mainly) doing exactly the same things you did with some success, but this hobby deals with life and life is always unpredictable, what works for one may not work for another.
That's all I can think of, I'm really sorry If I'm no help and for what's happening to you.
I truly hope you can get your tank out of this bad phase and I look forward to seeing it crystal-clear and healthy!