BGA is caused by excess nutrition in your water, especially phosphates. It is not an algae, but bacteria. You have a few of options to treat it. 1) Black out, 2) Antibiotics 3) Tear-down.
1) Blackout - remove fry, do a large water change and remove as much of the BGA as possible by hand, then cover the entire tank in multiple layers of black garbage bags so that absolutely no light is getting to the tank. Keep this cover on for 5-7days. After removal of the bag, the remaining bga should be dead and your plants may look a little sickly. Do another massive water change. Wait for water to stabilize. Reintroduce fry.
2) Antibotics - The use of medication and chemicals to treat anything besides fish sickness is not advisable. However, Maracyn (antibiotic) has proven itself to be effective in the treatment of BGA. Just buy the powder. Make sure it is MARACYN, not Maracyn 2 or any other variation. Remove fish fry, and remove as much BGA as possible by hand. Follow dosing instructions of Maracyn (I think its 1 pack a day for 7 days). Do a very large water change at the end, like over 90% if you can. Add water, wait for it to stabilize. *****BEWARE: this method nukes some of your good bacteria as well. Because fry are extremely sensitive, I would not re-add them until you are sure your tank has returned to its previous matured state.
3) Tear-down - What you did before, remove everything, scrub and clean everything in hot water. Plastics and glass parts can be dipped in a 5% bleach solution (if you do this, you must scrub it again in hot water and let the parts sit out to dry 100% before reintroducing to the tank again). DO NOT BLEACH ROCKS or any other porous decor. Put everything back into tank and let it cycle again.
All of these solutions require you to remove your fry. The blackout causes an ammonia spike, the antibiotics cause stress, and obviously a tear-down cant have fish in it. Depending on the maturity of your fish, it may be wise to just remove the BGA by hand until your fish are a bit more mature and then move the fish.
To keep the BGA away, you should be doing more frequent water changes to reduce the amount of excess nutrition in your water. You should see how much you are feeding as well, excess food is a huge contributor. Lastly, check your lights, excess light causes algae blooms, bga or not. You can also try adding more plants to help keep the nutrient levels down and improve water quality. Additionally, plants like anarchris and Hornwort
have been shown to release alleochemicals that discourage BGA growth.