120 in the Wall

[Ginu]

I think the most cost effective would be to use some sort of a two part system controlled by dosers. I tried looking around but didn't see anything in regards to an aquarium comp, are you using any?

For example I'm using apex which does the monitoring and in that I have two dosing pumps from BRS and they dose alk and ca. I dose mg manually as it takes quite a bit to dent magnesium.
In my new system I'm going to dose zeo products which will be done manually.
I've also preordered a apex dos which will take care of water changes so I recommend looking into that as well.

Also dosing systems are good although I've never used one, but a bubble magus or vertex or any other reputable brand will do the trick.

In regards to lights, that's a huge topic and it all depends on budget and preference so its tough to pick one.
The new trend I see is LEDs and t5 although some reefers love their halides so its very debatable.. On my 34g cube I had a 150mh producing a ton of heat, on my 75gal I went with two radions which I liked but hated taking pictures under and on my 120 I'm going to try a ati 6 bulb fixture, would like a ati6 bulb hybrid with LEDs, but that ain't cheap...