oh and source is ro di

I am not sure why everyone thinks that 1.022 is too low for SG reading. Myself and a few of my friends all keep our SG at 1.022 in my SPS reef and I have never had a problem. I know a LFS here that keeps it at close to the same level as I do as well.
Can anyone fill me in?

It's not that 1.022 is low for a system; i don't personally see a problem with that. The problem I see is that if a coral (or anything really) comes from the majority of the stores who keep their water at 1.025 (notice i said "most" this time :)) it has to very quickly adapt to 1.022... essentially its getting the salts sucked out of it by osmosis. Even with proper acclimation for hours, I don't know... but hey, that might not even be *the* problem.

So I couldn't find where you mentioned the Temp of your tank. High and low or if it is constant. Also are your corals bleaching? or do you notice a brown jelly, white paste? black gooey material? ect..
I ask where you place your new coral and bulb age because of burning. If you get your corals from the same place, that happens to have low light and the tranfer to your tank with bright light, now where in the tank may be safe from burning esp if your tank depth is low and your lights are close to the water. Just a thought.

I still say if you go to the Zeovit.com web site and say that your Alk is 10, they will tell you to get it down to NSW readings. It has to do with the way the bacteria work in the zeo system.

I agree that you should look in to lowering your alk if you're using Zeo (but if you haven't been using Zeo since you started trying to keep SPS then this won't explain your problem).

Again, check your SG with a refractometer - not a "calibrated" hydrometer. You can't believe the number of times people have assumed their "calibrated" hydrometer(s) were accurate only to find they either went bad or were never good (Brad can attest to this). The problem may not be that the SG is 1.022 but I would be surprised if it actually was 1.022.

Flow coming from the sump "at some astronomical rate" doesn't tell us the flow rate. What return pump are you using? What is the rated flow for the return pump? How high up does the pump have to pump? How many elbows are plumbed into the return pump plumbing? Those Koralia 1's are inadequate in a 75g.

I would stop assuming your Mg is ok. If you can't get a test kit locally order one from J&L or Ocean Aquatics - they're both close and shipping will be relatively cheap.

When was the last time you measured the TDS of your RO/DI water?

Have you ever added any detrivores to your deep sand bed? I would guess your deep sand bed is a sewer dumping nutrients back into the tank as evidenced by the fact that you continue to have hair algae. You 100% do not have zero phosphate if you have hair algae growing in your tank.

So again, I implore you, if you want help figuring this problem out take a picture of your tank and post it here so we can stop guessing and see what we're dealing with. Trying to "diagnose" your problem without seeing at least a picture of your tank is just going to beget more guessing.

I agree with this theory as we'll. I kept my dkh when i was running Zeo at 7.That could be a issue.

What is the TDS coming out of your R/O?

You say they die from the bottom up. How quickly? Is it RTN or STN? In my experience if corals are dying from the bottom up they are either getting too little flow or too little light or both. I can assure you that in a 75 gallon tank you are not even close to the flow you need for sps with your current power heads. IMO those KH1's are barely enough for a 20 gal nano. As an example I have 2 sieo 820's & a Tunze nano stream (1200 gal hour) in a 40 gal frag tank.
It's a big jump going from a FOWLR or Soft coral reef to sps because the requirements are very different and flow & lighting are key in keeping sps healthy.
Also what brand of salt do you use? Have you tested the new water mix and if so what is it at?

What do you recommend for flow in a 75G for SPS Greg? I am getting about 44X turnover (3300GPH) in my 75...

To put the flow thing into perspective I have a maxijet 1200 with the mod kit on my 65g (same footprint as the 75g but only 18" high) so thats approx. 1600 gph flow on a tank that has my tube anemones, bubble coral, fox coral and mushrooms, all low flow corals.
If I was going to have sps in there I would add at least another modded maxijet.