Day after Algae appears, help!

[Roundeye]

Does anybody have any suggestions about the algae that appears after 15gallon water change. Tank 50 gallons truvu, additives added calcium,iodine.(reef tank & fish )
Thanks--John

[leebca]

A bit more info would be helpful. What does the 'algae' look like? Are you sure it's algae? What kind(s) of filtration are you using? LR? substrate? Have you checked your source water for compounds containing nitrates and phosphorous? Do you know how much nitrates and phosphates are in your salt mix?