Finally some Algae in my ATS

[Levinson]

Not sure if this post belongs to New to Saltwater forum but since I am new to saltwater and this being my second post in R2R, I'm posting it here.
It's been almost 3 weeks since I ran my first DIY ATS, about 10 days since I've added my first, very small bio-load (20 lugworms) to the new tank, about 8 days since I rubbed some random green algae onto the screen (in attempt to seed it) and I think I'm finally starting to have some algae along with a slight drop in nitrate level.
Not seeing any sign of algae or any change for a while, I was starting to get worried (hence seeding and all) but it seems it's going somewhere at least.
Sorry about the crappy photos.

 

[reef lover]

Sweet!

 

[Levinson]

UPDATE: This was what it looked like earlier today (4 weeks since I had ATS running, no water change, only top off)

IMG_20200516_140138.jpg

IMG_20200516_140148.jpg

Mostly shades of dark green with brown and red bits or lumps. You can also see some no-growth spots where the bulbs were (photo-saturation?).

...and this is after cleaning it (for the first time ever). Not 100% sure if it was a good idea to clean it. I was starting to have some light green algae but I read the dark green/brown stuff should be removed when you can. Maybe I should have left it to grow a bit longer?

IMG_20200516_142216.jpg

Over the past 2 weeks, the nitrate went down for a bit then back up again. Something like 120ppm -> 80ppm -> 40ppm -> 40ppm -> 80ppm. This seems a bit odd to me. I have very small bio-load and don't feed much (20 lugworms with a pinch of feed once every 2~3 days).
Could the reasons be any of the followings?
- there were too little algae to make a difference.
- something in the tank may be rotting away somewhere.
- the top off water (not treated and contains nitrate 20ppm) is the cause of nitrate increase.
- faulty test kit.
- not enough bio-load/nutrients for the ATS to really work properly, even with high nitrate levels.
- not enough phosphate limiting the algae growth.
- it's just me being hasty again and should just give it more time.

The only inhabitants in the tank are still the lugworms. I'd like to bring the nitrate level down a bit more (0~20ppm) before introducing any others into the tank. I don't mind experimenting with the worms in the tank BTW (sorry not sorry worms, you guys were being sold as fishing baits).
Also, does raising phosphate level help ATS algae growth? I'm asking because I was given Neophos from Brightwell (phosphate in a bottle for aquarium) and was wondering if it'd be a good idea to put some in. I don't have a phosphate test kit so I don't know its current level. If it promotes the growth of dark slimy stuff, I won't bother.