With your comments, it sounds like you know what you need to do... limit nutrients. If you're using tap water, a RO
system would be my first move. You mention a control unit for your lighting... are they not on a timer now? How long are you running them?
Is your skimmer pulling any gunk out of the water? If you aren't already, running some GFO
(granulated ferric oxide) will help reduce/eliminate your phosphates and silicates if you have any in the tank.
How often are you doing water changes? And how much are you changing?
And yes... phosphate levels, as well as all other water parameters (nitrates, pH, etc) will need to be known to tell you what you need to attack.
Welcome to AA, by the way!