I have a UV (Turbotwist 18 on a 55) on 24/7. Trust me. It doesn't work
Ditto we long tried this, back in 2000 or so.
It was on a 50 gallon with 110 w of light that I first saw this alga.
He had a 15 w on a 50m gal tank without success and he cleaned all the time.
He has a nice filter as well.
I had a lot of troubles inoculating GDA. Only in recent times have I been able to induce, thus confirm, some possible causes.
If you do not confirm and induce it on purpose, it just happens and then you try and go back and figure out what you did, that's a poor method.
I'm finishing up with the Cladphora right now, and did two pilots for the GDA.
It comes back more when the CO2 is lower, and when you add ferts, there does seem to be a relationship between fish load and the alga, it might respond to NO3 more and decrease to NH4.
That's not an easy balance and it's subtle at best.
I have several tanks, and some will just not get GDA no matter how many times I inoculate. Same filter, same substrate(ADA AS), same lighting, same ferts etc, plants are different but I do not think it matters.
Lighting seems to play a large role, especially in the middle ranges of the spectrum.
But that too seems not apply, as I've had it go away with the same lights in a few weeks etc.
I've also seen it decline with repeated attacks weekly.
One thing also: repeated attacks also have been very effective if the plant health is very good, it left in 2-3 weeks just doing that in several tanks.
Folks with MH's do not seem to get it, namely just PC lighting.
Temp is not it either.
The let it run it's course worked for me, although if I allowed direct sunlight, poor CO2 etc, general neglect etc, it came back.
I think what bothers folks is that it goes away sometimes on it's own without any really action from us.
I've been able to induce it with higher light and poor CO2. Direct sun worked very well. It's patchy where it grows and then later can over take all the glass, loves light and glass.
Substrates do not matter. NH4 may play a role. Cycling/bacteria may as well, herbivores(microscopic) also might play a role.
I do wonder how well folks made sure they had everything in terms of their CO2 and ferts(easier than CO2 to rule out). The issue of CO2 right at the start of the day is another possible problem for inducing it.