Blocking out the tank will not do the job because you're not exporting the nutrients, sure you kill all the algae but without removing the nutrients it is just going to come back when the lights are turned on again.
Rowaphos, harvest heavily and build either a refugium or an algae scrubber in the 2nd compartment. Put the rowaphos in the last compartment so the algae scrubber does not starve.
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