You’ve got more than bba in there. Looks like some sort of spot algae. What are your nitrate readings? What are all your reading? Siamese algae eaters may eat some of that but being a 30gal all you’d want is 2 for that size tank.
Probably algae eats all nutrients. Do you use fertilization? Remove all alge that you can with brush etc. Ornament dip in some bleach solution, wood get out of tank and use peroxide. Clean your tank very good, wc, gravel vacum etc. Remove dead plants, leafs and other organic stuff. Then buy some plants, I don't know what exactly plant I would recommend but tropica have some like starter bundel or go to local fish store and ask for some begginer fast growing plants or just google it.What are some plants you recommend? Do you know why my sag isn't doing very good I'm using root tabs