I mean... as is, this is beyond "fixing" without a complete teardown. If I were you, this is what I would do:
1.) remove any livestock to a quarantine tank, and hook your filter up to that tank
2.) pull all plants you intend on keeping
2.) fill a bucket with clean, dechlorinated water, add a cup of H2O2, add plants, and let sit (6 hours max)
3.) syphon all of the water out of the tank
4.) remove all of the hardscape, scrub with toothbrush, rinse, and soak in the bucket with the plants
5.) remove substrate, and rinse thoroughly with dechlorinated water
6.) scrub all surfaces with clean water
7.) add substrate back into tank
8.) rinse hardscape with fresh, dechlorinate water, and add to tank
9.) remove any dead or dying plant matter. replant anything that looks healthy
10.) fill with 100% new water
11.) move livestock over
12.) thoroughly clean filter with dechlorinated water and move back to display tank
13.) moving forward... WATER CHANGES, REDUCE YOUR LIGHT, and KEEP YOUR TANK CLEAN. This didn't happen overnight, and now it's out of control.