Tom is right (of course). I started using his reactor design a few weeks ago. Prior to this I used an inverted bowl design, a DIY reactor similar to the one you are having issues with (sponge, tube, powerhead) and the intake to my HOB filter. The intake of my HOB worked the best out of those option....but even then I was only getting around 18-25 (using a ph-kh chart). Now with his venturi reactor design I am seeing levels of 40-45 ppm. No algae.

You need to dose KNO3. During the blackout and after!