Did I kill or can I kill my purple coralline algae?

As you may have read in other posts my tank was very neglected for a long time, water quality was never very bad, but I was running with old, half burnt out lights for probley 6 months, and water quality was not great. Did this kill my purple algae? I have good lights, good filtration, and good water quality now so will it come back, the rock used to be covered by purple carline. Or do I need to get some seed rock to re grow it?

It'll likely come back on it's own, but slowly. Coralline algae is calcareous and needs calcium to grow properly, so you might need to add supplements to your tank. I use the B-Ionic series and it keeps the Ca level in my reef tank around 420ppm, which is good for coral and coralline algae growth. Maybe your levels are high enough already; there are plenty of test kits for Ca and they're pretty reliable

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When in doubt, do a water change.