Corraline is an indicator you can support calcification and if you just have algae you have no indicator . Sure it sucks but right now you are guessing with frags
I'm only about 1.5 years in to reef keeping but I made a very similar decision when I started my tank. I bought a Duncan and for a few months it was doing well but my tank was very immature. I think I added the coral at about 4 months. At 6 months with dry rock I got into the Cyano, GHA phase and both of those algae consume the nitrates and phosphates that your coral need. My duncan died along with the others I had added because the Duncan started off so well. It's okay. Others have been through it. The key to reef keeping is patience. Let your take mature a little. I waited until my tank was 1 year old to add coral again and my tank is full of coral and it is doing quite well now. Good Luck!
something’s not right with the RODI if it’s reading 5, that’s still too high, should be 0-1. What unit are you using?
looking at those frags they are prob not going to make it, the monti is already dead. If you can rehome them in someone else’s frag tank they might pull through but your tank isn’t ready for them yet.
sucks, but jumping too early on coral before the tank proves to be ready is a common mistake most of us have made. As others said, waiting for some coralline is a good indication things are balanced out and in good order.
what fishstock do you have? The excess algae might also be attributed to running your lights longer or brighter than needed