Why are you keeping phosphates low??? By that i mean your Po4 values in the water... get it up to 1-2 ppm!.
Also once this algae (BBA) sets in it doesn't magically disappear when the water conditions change to a better one for plant growth.. they will still stay there.. they just wont "multiply" as rapidly. You have to manually remove all or most of what you can see and then make sure the water condition is good enough so that your plants grow well..
Mostly this algae is caused by a problem with co2.. check and recheck that again.. you can try cranking it up a little more and see if the fish start to surface breathe..
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