Dealing with algae on a severely neglected tank

I'd put a bag of GFO or chemi pure elite in the filter, vaccum the substrate if its possible, a few big water changes, may need new bulbs if you haven't replaced them since before sandy.

I'd do 25% water changes per day for a week, then cut it down to every other for a week, then do 50% every three days for two weeks. That will definitely help bring the tank back to life.

Algae-specific I think that Japanese Trapdoor snails would devour that, but since I haven't kept them in literally forever I'm not entirely sure on it. I'm not 100% sure on the algae species, but I know for some kinds you can take it down a notch or two by cutting back the time your lights are on. I don't use chemicals so I can't advise on that, but worse come to worse you can always scrub the algae off manually with some unused filter media and rinse the plant/driftwood in some tankwater during a waterchange.

Glad to see that you're coming back into the hobby.

Since you still have fish in that "old" water, It's best to do small water changes maybe every couple days and closely monitor water params to avoid big changes. I wouldn't use any chemicals to get rid of the algae. Manually get rid of all you can then add lots of snails to finish the job. I like ramshorn and apple snails. They seem to be readily available from like CL. The snails have done a great job for me.

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I see some black beard algae, which is pretty hard to remove in my experience. Once you get the tank back on track it should not be a big problem. I don't know what that algae is on the anubias and java ferns though. I have the same problem but have not managed to fix it in my tank.

I had the same experience with BBA taking over an unattended tank. I did 3 things that helped a lot. I'll list them and then explain details of why they worked. NO CHEMICALS... Create balance instead!

1. I planted water wisteria in the tank. Lots of it... and I let it run wild! Trim it back a little and let it go again.

2. I introduced Siamese Algae Eaters (SAE)... They love the BBA, and they are one of the only fish that do.

3. Water Changes. Increase frequency for a while, but 25% is fine.

Explanation:
Planting fast growing stem plants like water wisteria that can handle lower light gives the algae some competition for nutrients in the water column and the substrate. (The water column nutrients are more algae's style, so focus on them.) Many people suggest floating wisteria, which has benefits too, but I suggest planting it in this case because it will send out runners and grow bigger, faster, better to help you with your problem. It's also pretty much indestructible, and if the BBA develops on its leaves, just pull them off and toss them... won't hurt it.

SAE will grow to about 6" which would be fine in a tank this size. They aren't a great suggestion always, but they will help you out tremendously. Keep in mind their future size, because I have never seen them over 2" in a LFS... it can be deceptive. Mine have at least doubled in size from when I bought them. They are pretty fun to watch too! Be sure that you get "true SAE" or they may be a variety that opts to leave algae behind as it matures, and then it's just another flake eater. You can also safely cut back on feeding the whole tank to encourage algae consumption and reduce nutrients being added to the tank. Your fish will be fine if you skip feeding every other day for a month to get things under control. They will give you dirty looks... don't cave!

Since it's been neglected, 25% per week will be an upgrade when it should have been more like a water change routine. I don't suggest drastic water changes unless there is a MAJOR problem. This is not pretty, but lets not rock those fish's world too much. Also, that's a lot of water! Set a scheduled day and STICK TO IT! After a month, you should see a big reduction in BBA. After 2 months you will think it's gone, but it's not... it's just reduced. After 3 months it will mostly be gone and will no longer be a problem because you will have achieved balance.

Good luck! I hope all of this has helped you on your quest to beautify your tank. Don't give up!

Gotta keep the fish in mind here, too...