This was my tank a week ago, I’ve had it for about 8 months and it was thriving, had a lot of pond snails, 6 flame tetras and 6 zebra danios. I never did water changes and just Topped it off with dechlorinated water. I tested parameters every few weeks and never had any issue.

Two days ago after I topped it up with some water, all of fish started floating to the top and gasping for air. I panicked and did another water change thinking it would help and watched it for a few hours. I turned up my air stone and it seemed to help as the fish stopped hovering at the top and went back to exploring.

Fast forward to today, the tank has no signs of life, has weird pockets of white biofilm in places, algae in most others and the plants are now melting.

What the hell did I do to my tank, what do I do to fix it?

I’ve had small losses before in this hobby but this is the worst loss I’ve ever had and I’m so gutted. I loved this tank, I was so proud of how it was doing.

Pic of today in a comment. If anyone has any advice at all of where to go from here, I’d really appreciate it.