Coralline algae is a good indicator of water quality. Assuming all Ca, Alk, and Mg levels are as they read I strongly suspect PO4 and probably NO3.
Sounds like your lighting is a bit too dim to maintain good growth and colour for SPS. You may want to try supplementing with an extra strip or switching some of the dimmer bulbs (fiji purple or blues) with ones with higher par values.
Also, if you're feeding everyday and only doing 10% weekly w/c your skimmers cannot keep up with the nutrient export.
Bio balls are unsuitable in a reef tank because they create NO3 that cannot be converted fast enough, with a better test kit I'm sure it would yield NO3 readings.
First thing to do before you do anything is test the water with new reliable test kits.
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