When I bought my skimmer, I was told to always get one rated for twice your tank size, because most skimmer manufactors overrate their products. What brand/model is it? Second your phosphates and nitrates are low because they are being used as fertilizer for the HA. A skimmer is a good start but only a start. Are you using RO
water or tap? Have you had the RO
water tested for TDS
? How old are your light bulbs and what type are they, how long do your lights stay on for? How often do you do water changes and how much do you do? What size is your tank, what fish do you have, how often and what are you feeding what kind of CUC do you have? HA is a PITB but the battle can be won. It will take monthes to get rid of it completely.