Hi,
Thank you, tank is 18 months old, I have been doing 15% WC every 6 to 8 weeks.
Good skimmer imo is important in fowlr, I also have brs reactor, after 6 months I stopped using GFO only GAC.
No algae problems since day 1, which is why I keep light CUC, few snails, most of them die because of lack of food source.
And finally probably most important advice I got from one and only SDguy, since I enjoy that tank only in the evening (I have two 3 year old twin boys with health problems, so I am busy during the day-home stay dad) I only have tank light 3-4 hours a day from 7pm till 11pm. Day light or room light is perfectly fine for fish, they see what they need to see

But thanks to that brilliant advice I clean my tank acrylic panels once every 16 to 18 days, heck that tank makes me lazy
Feeding twice a day, tank is overstocked, no issues with water quality or algae, planning bigger and better etc.
Give it time and your coraline should start spreading.
But I also have to say my 50g reef has much less coraline with all alk and calc adds, LEDs may be a problem (just a guess though).
Good luck
ps-somebody told me coraline algae likes shorter periods of lightning, not those 9-10 hours days, in my case works perfectly. And no, I do not have any other proof for that, just a word from a friend who has been in the business for the last 20 years, maybe he is right...