Looks like diatoms to me, which are very common in new setups. If they appear in an established tank then there's some sort of imbalance going on. High Nitrates/Phosphates can be the cause. Test your water, if you have high Nitrates then do more frequent water changes, and eventually it should become less of a problem. There's yellowing on some of your plants which indicates some sort of nutrient deficiency, you could look into dosing liquid fertilizer and some root tabs for the swords and other stem plants. Some kind of algae eater could also help with your problem, amano shrimp and otos have helped in the past, though otos require a more established and balance aquarium in my experiance.
It could also be green spot/dust algae, which I've seen turn a darkish colour in the past. If so, then doing more frequent waterchanges and cleaning would help. It might also help to reduce light exposure time and intensity, floating plants like duck weed can help if you have a non dimmable light.