I will admit,,,, pretty much all the people who have replyed in your thread know way more than I do when it comes to keeping SPS corals. I will also say that if I can grow SPS corals,,, anyone can grow SPS corals. I may not get as fast of growth as some/most, but I do get growth, and pretty much the only corals I kill, knock on wood, is when I don't acclimate a new frag as well as I should and try and rush getting into its forever home in my rock scape. Soooo, I am going to throw some advice at you here, with the disclaimer of, I am not a SPS Coral Whisper, I was where you are at with your system not that long ago, when it comes to losing corals and maintaining my system in a way to keep my corals happy and not losing them. If your system were mine ,,,, this is what I would do ,,,,,
The first thing I learned, stability is the key in keeping SPS corals,no matter what I do to my system, everything goes back to maintaining that stability in the tank ,,,,, same, same, same. First off I would, stop using your dosing pumps, I would stop dosing Kalk to your tank, I wouldn't run carbon, if you are and I would stop dosing SPS coral food to your tank.
When it comes to flow in your tank, I can't tell you if you have enough or to little, what I will tell you is this,,, Watch some You Tube Videos with SPS tanks. Look for how sps polyps react to the flow in those tanks & try and emulate that in your tank. A picture of your tank would also help in this thread, it would allow us to see if your rock scape is conducive to providing good flow through out your system. You don't want direct flow on your corals, that will kill corals just as quick as anything else, indirect is what you want, ask me how I know that
The fish you have in your system, 60g DT & 20g sump should provide enough food for your corals. You don't have a lot of fish, but you don't have a lot of tank either and a couple of those fish are good sized fish.
Water changes: You want to do away with these monthly water changes you are doing and go to weekly water changes. I would keep the size of the water changes to a max of 5 gallons maybe go up to 6 gallons at some point, but start out at 5 gallons. By doing weekly water changes, your tank will be more stable when it comes to Phosphates and Nitrates, they won't be climbing for a whole month before the next water change. Try and match the water for the change to as close as you can get it to the temps in your display tank. I start mixing my water with a large pump, mixes the water well, but the water temp gets up to about 87 with that pump. After I get the salinity where I want it, I switch to a smaller pump, and let it run for 24 hours, this smaller pump, over 24 hours will bring the water temp down to 78. The temp in my display tank is 79, so I don't have that big of a swing when I do the water change and it only stays there for a bit, until it gets mixed with the water already in the display tank.
Water Testing, do away with testing every three days as you say your are doing, you want to test every other day. My guess is you are testing every 3rd day and dosing your tank up to your target numbers, that's a big swing or at least a bigger swing than it needs to be, we don't want big swings, we want small swings. Test in the afternoon around 4 to 5 pm as best as you can.
Tank Parameters,,,, I may get blasted here,,, but I am sure I am sure I will get blasted for other things I have already said in this post

Make the target numbers in your tank ,,, Alk. 9.0 dkh Calcium 450 So, why am I telling you to make your Alk. target number 9.0 dkh when everyone else is telling you to make it a low 8 number. I was doing the same low 8 dkh in my tank at one time. The problem is water changes, the Alk. from the salt I was using was pushing my Alk. number up to a high 8 dkh number after the water change. Tank would take a few days for the Alk. to drop back down to my target number, a level where I could dose, if it did before the next water change. What you want to do is get your target Alk. number above the swings from the salt you are using. If you are having to dose even after the water change, you will be able to keep your tank more stable. I got that advice from a friend, has made my life a lot simpler
To run GFO or to not run GFO You don't have a large system, I suggest you buy this:
http://www.nextreef.com/images/Shorty/Shorty.jpg
Its a quality reactor & the size you need for your system. I would run GFO if I were you, not a lot, 1/2 cup at best. you will need to check your Phosphate numbers for a time to see just what your numbers are at. I watched a video yesterday about Phosphates where the man giving the lecture said even a 1. something Phosphate number isn't a bad thing. I am sure he is right, but not being a " SPS Coral Whisper " what I am wanting in my system is stability, even when it comes to a Phosphate number. I couldn't tell you the last time I checked the Phosphate or Nitrate numbers in my tank. I let the corals tell me what I need to do at this point. I am sure I over feed my fish, not to the extreme though. Corals are alive and growing so I really don't care at this point what my Phosphate or Nitrate numbers are at.
Lights,,,, this is a tough one, so many brands of lights putting all different levels of Par into a tank, and the depth of your tank comes into play also. I started off with AI Sol Blues and upgraded to Hydras. But,,,to give you a easy,,, simple,,, answer here ,,,, if you are using LED light which most people with new tanks are using, this is what I would do, you are going to have to play with this and let your corals tell you what you need to do, keep in mind this is just a starting point with your lights. Place your lights about 10 to 11 inches over your tank, don't run your white lights more than 40% of their capable percentage. At some point your you will get the feel of what your corals can take & most likely raise the light percentage. We just don't want to be killing corals with your lights which is a easy thing to do.
I am sure I am not addressing some issue here, but doing this stuff has got me from where I was at, like you, killing corals, and onto being able to keep corals alive. Always keep in mind, stability, the smaller your system, the more you need stability and smaller the swings in your tank you can have. Always think same same same