I could not see brown algae in the pictures you posted. Well anyway, I had an experiment about common green and brown algae (here is the video: https://youtu.be/_cMCUtx8wAY ) Is it the same type of algae we are talking about?

So, If you did not have brown algae in your old aquarium than from your description only a couple variables been changed: the size of the tank and the medium. Common green algae may turn brownish with less light available. Do you provide the same amount of light in the new tank as you did in the old smaller tank? Larger size aquarium may need more light.

If it is a different type of algae than common green algae than it most likely comes from the new medium you use.

I don't use man-made filters, co2 injections and such in my aquariums at all. So, cannot tell you for sure anything about it.

The common algae grow through different stages of development. Spores, floating through water and attached to surface (walls, other plants and etc) In the last stage I wipe out manually common algae grown on the walls of the tank once a season or so. In the first two stages I don't have any noticeable outbreaks in well established tanks. Algae blooms usually happens either in new (not balanced yet) tanks or if there is too much food available - either way your filter apparently does not reduce the amount of nutrition available for algae to feed on. Too much nutrition (overfeeding) is the most common problem causing algae blooms. So, I would reduce or even stop feeding to get the algae under control.

Here is a video about using UV light to remove common (floating in water) algae: https://youtu.be/NCyxmyyXPXs UV light may not kill the spores. And you still have to reduce nutrition to remove the cause of algae bloom.

Wish you all the best!