GHA and new Odyssea MH pendent

Forgot to mention that I do 10% water change weekly. I did look closely and didn't see any branching at the tip of algae so I'm pretty sure it's not bryopsis.

 

Here is my action plan:
1. Already order a Phoenix 15k 150w DE bulb from ebay. Questions: will my stock Odyssea ballast fire the bulb without any issue? Do I need to change out the stock actinic T5 as well or they are not as critical?
2. Already installed a 13 w UV temporarily which was laying around in the garage anyway. Do you guys think it will do any good?
3. I have a two stage household Kemore canisters laying around. I'm thinking to order two modified refillable cartridge from bulk reef supply with Purigen on the first cartridge, and GFO and carbon on the second cartridge. Is this the correct order: skimmer -> mechanical filter (sponge in Nano tank) -> ceramic rings -> bioball -> Purigen -> GFO -> carbon -> DT. Do you guys have any experience with bulk reef supply's carbon and GFO? This setup will be overkill for the 24g nano. If I have success, I'll then take this setup to my 55 g tank and set up a one-canister for the 24 g.

Thanks for you guys' value input.