Let me tell you my experience with this SOB.
About 2.5 months ago, i really suffered from diatoms. This was not the first initial diatom bloom that almost all tanks get. It came back. And it came back hard. So the reason why it came back was cuz I decided i wanted to lower my substrate near the front, but i did not want to remove my aquasoil that i had capping my flourite. So i decided, lets move the aquasoil to the sides, scoop up the flourite, then cover back with the aquasoil. Well, it worked, but at a huge cost. I am not sure if I did a WC after that but i think even if I did, I had already mucked up my substrate way too much. Diatoms came about 1 week later. It remained for 2 months. During these 2 months, i thought about ragequitting this hobby since I couldn't figure out what was going on. I kept arguing "its not diatoms! I see that the glass is pretty clean and browning only happens around the edges of some plants, but it does not wipe off". I found out i was overdosing EI, so perhaps it was overdose of ferts, and i reduced my dosing. I also had gotten a new light, the Kessil LED. Perhaps it was too much light. I also changed to a canister filter, maybe i wasnt cycled anymore. But here's the thing. Overdosing ferts has been proven to not be the cause of algae blooms by the majority. Kessil LED's PAR placed me around low to medium light. Filter shoudlve built up the bacteria pretty quickly as it also lives in the tank and can colonize the media quite rapidly. The only reason left was the substrate swapping I did.
So I increased my CO2 as much as I could and dosed regular EI. I started getting hair algae, cyano, staghorn, and BBA all along with these stupid diatoms. My tank was a mess. It got to the point where my plants were too unhealthy to continue. They were surviving, but it would take a long time for them to recover. I decided to finally do a blackout. 3 days, 0 light. I did not care about the plants since i figured if they die, they die, i cant do much about it, they arent going to live much longer anyways.
I uncovered the tank. All the browning went away. Clado was hit hard, so was hair algae, but it was still there. But the diatoms were gone!. It took me about 2 months to decide to do the blackout. Over the next few weeks, i got new plants in, used my old wisteria i kept alive in a bucket to help the tank recover, removed as much algae as I could and tossed plants that were too badly infested. Kept dosing EI, CO2, etc. Still had hair algae, spiro, and clado, but algaefix worked wonders.
To this day, the only algae I am battling with is BBA and I know why. Plants are doing very well and growing fast. I still dose EI and even double my phosphates and micros. No diatoms, no algae other than BBA. I learned from this experience to focus on growing healthy plants, not killing algae or controlling it. The plants when doing well will cover that for me. But first you need to get healthy plants in or have enough.
For the diatoms, try to be patient. Don't expect them to go away even in a months time. Keepup with good filter cleaning, maintenance, stable CO2 and water levels, add more plants, and Water changes. Blackout if you cant stand it, the plants should handle it no problem. I even had UG blackout. No problems, just a bit of it turned white. Eventually, you will see them go away. I want to suggest just black it out, then add in tons of fast growing plants to help stabilize the tank. But I also believe time is very important to defeating diatoms.