I run lighting 10 hrs total. Actinics for 1 hr and then halides come on for 8, then another hr on the actinics. Then lights out.
Based on your water quality being perfect (not sure if it is), if its browning it is probably because it wants more light. That is usually a symptom of the brown color. If it was bleaching (turning white) usually a symptom of too much light.
Try increasing your lighting time to 8 hrs, but do it slowly over the coarse of a week or so. See if it starts to color up. Wont happen over night.