I have a fully stocked sps tank . Evrrything is doing great except my acans they have all started to die off. I purchased a new skimmer about 3 months ago and brought my nitrates almost down to 0. Before the new skimmer nitrates were about 15 -20 ppm . Tank is a 130 gal 400 watt bulbs acans placed at the bottom . Nit 5 cal480 mag 1650 kh 12 . What should i do.