I dealt with a massive ulva outbreak early one that was similar or even worse than yours. Here are suggestions, most of which have already been mentioned:
1) Manual removal. There is no more effective clean-up crew than human beings. I use an electronic, rechargeable, waterproof grout brush from
Amazon. Be prepared to do this once to three times a week. It is preferred to remove the rocks and do this outside the tank. This can be cumbersome so it is fine to do in-tank removal paired with large water change and relying upon your mechanical removal to cleanup the water column. You need to get the algae to a short length for your CUC to be effective.
2) More cleanup crew. Specific recommendations are a mix of 35+ snails including turbo, Astrea, Trochus, etc. Get a wide variety. I got one inch turbos and had 6 grow to 2.5-3.0 inch in size. I ended up giving most of them away once my algae got under control. I replaced them with smaller species of snails. Also get at least 2 urchins. No other cleanup crew can shred algae from rocks as effectively as they can. If you don't have one, get an Algae Blenny. Those guys are super hard workers. Tangs are also useful.
3) I would also stop with the Rowaphos.
4) Don't rush into getting coral. Start with a few cheap LPS and see if they survive. You have a lot of coraline algae so should be able to grow coral.
5) For CUC, try to keep them off the glass and on the rocks. This means moving them manually from the glass to the rocks and keep the glass (including the back glass) clean so they aren't tempted to hang out on the glass all day. Every CUC member on the glass is one not doing any rock cleanup work for you.
6) I recently got a lettuce nudibranch. Seems to be working hard all day. I wish I got a second one for my 110g display. They sell them on saltwateraquarium.com. I prefer to order from them since the specific come in very healthy and clean. ReefCleaners has wider variety and sometimes better pricing but have a rougher time in transport to the West Coast where I am.
