Raise FC immediately! For CYA of 40 you should shoot to maintain 5ppm FC.
Also, you might want to lower pH a tad (shoot for 7.4-7.6) using muriatic acid (31.45% concentration, not the low concentration "safe" stuff).
My only experience is with a vinyl pool, but if I understand correctly, with a concrete pool you'll want to raise CH to at least 250. Hopefully someone with more knowledge of concrete pools can chime in.
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