dosing is your best bet. I use ATI Essentials which I love. 3 different liquids I dose and its really a no brainer. I test weekly to see what I need to tweak, but haven't had to do much and my growth is great.
I also used BRS 2 part (alk and cal) which worked fairly well. Theres a lot out there on dosing. Get a high quality dosing pump, like Kamoer or GHL and dose/test, test/dose. There are also calculators on Bulk Reef Supply.com to help you with how much you should dose based on tank size, but realize your intake of the elements has a lot to do with how much you need to dose too.
I would dose before you mess with reactors which aren't as plug and play as one would like.