Welcome - IM Lagoon looks like a great choice for what you're planning. I am running a 14g Mushroom dominant tank. they are so much fun. I have a single AI Blade 21" at about 16" from the substrate (my tank is fairly shallow). I think I am getting around 75 PAR on the substrate and 150-175 PAR on the upper rock work.
I test weekly and do weekly 10% W/C, 10ml frozen food daily with target feeding and 0.01ml ELIMI-NP daily carbon dosing to mange PHOS and Nitrate. Parameters are the following:
Temp: 77.9-78.0
Salinity: 1.026
Alk: 9DKH
pH: 7.9-8.1
AMMO: 0.0
NITRITE: 0.0
NITRATE: 16-20PPM
PHOS: 0.4PPM
Ca: 416
Mg: 1159
I have seen tremendous growth on Neglecta, Disco, and Riccordea. I struggled with a Yuma but I think this is because I placed it at the top of the rock scape and it bleached out. it is still hanging on but if I lose this one i'll chalk it up to learning the rules of the road. Additionally, I am working on a plan to raise Mag to 1300-1400 but have not implemented a means to do so yet.
My approach might be a little more hands on than what you are looking to do but I think the beauty of mushrooms is that they can thrive in and acclimate to many different conditions.
One takeaway that I would emphasize is to set your lighting schedule and just leaving it. I have noticed my
mushroom corals are the most unhappy when I try experimenting with different schedules and spectrums. Like others have said in other posts and on YT, if you do want to increase your lighting, do it slowly over time maybe 5% per month until you get to where you want to be. Anecdotally, I impulsively increased my white light spectrum by 20% all at once and noticed some shock/retraction from most of my mushroom corals

. I have corrected and learned from my ways and things are back on track.
If its in the budget 2X of the 30" AI blades would probably be awesome but I am no expert - just a fan of the blades and the look.
Good luck and keep me posted!
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