I've got this stuff too Rich, but only in the coldwater tank, and it's a pain! To be honest I have tried everything I can think of to get rid of it.
Thinking the diatoms were due to not enough lighting, I increased the amount of time the lights were on and then got green algae as well as the brown stuff. Nothing worked. I have increased lighting, decreased lighting, changed the time the lights were switched on/off, cut down on feeding etc, etc.
The one thing that did work was following advice from Mary - take the fish out, empty tank, give it a really good scrub, clean all ornaments thoroughly, all plants etc. Wash the gravel too.
Replace with clean water, put the fish back in. Have lights on for no more than 4 hrs a day.
It worked a treat and completely got rid of brown and green algae.
Me being stupid then decided to put live plants in and so now have to have the lights on for longer and guess what? Algae, green and brown!
Good to have you back Rich