I made a big mistake... any suggestions on help?

I've got a 55 gal reef tank, and to make a very long story short, my wife and I do a 40% water change about every six months. Well this time we got crossed up, and after taking out about 18 gallons or so, we accidentally replaced it with NON SALT R/O water. I didn't realize it until today when I noticed some of my corals weren't opening up at all.
I just checked the specific gravity and it is at a dangerously low 1.015 or so.
This would explain why things aren't looking right.
I just pulled out three gallons and am replacing it with a R/O Salt mix as we speak. I was going to do that daily until I get the SG back up to its usual 1.025 or so.
As for my corals, they are some watermellon zoo's, a few button zoo's, and a frogspawn. Do you think they will make it?
If any of you have any tips on anything else I could be doing, I would certainly appreciate it.
Thanks to all who reply.
 
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