Advice on what to do with tank after total loss?

Unfortunately Luke, my Betta, passed away yesterday. We got back from 2 weeks holiday (I’d done several large water changes of 60-70% in the run up) and he seemed pleased to see us when we returned. The water wasn't bad for having not been changed whilst I was away, but I still did a large water change (75%).

But after a couple of days, he started looking pale, was lethargic and not interested as usual. I was going to come on here for advice (while doing a water change) as on Sat evening I noticed his scales looked to have lifted away from his body and he became bloated. But yesterday he passed on, as did his tankmates, a couple of cherry shrimps who he’s lived happily with for 8 months!

The shrimps had a white ‘fuzz’ around them when I discovered them. Obviously I’m very upset by losing them all, but was after advice on what I need to do with the tank before I can consider anything new going in.

I have several plants, a coconut shell and a piece of driftwood (see pic); which ideally I’d not lose too. Is it a case of stripping it all back and starting again or will regular, large water changes remove anything bad that may be present and allow me to keep the plants and decorations?

Any recommendations are welcomed.

Thanks,
Baz

There are several possibilities as to why the fish and shrimp died.
Whatever you did to the tank when you got back killed the fish.
If you added a heap of food it might have caused an ammonia spike and they took the fish and shrimp out.
The tap water that you used for the water change had something bad in it and that killed the fish and shrimp.
The bucket/ container used for the water change was contaminated with something.
The fish had TB or another underlying internal infection and it got sick and died and it was coincidence that it happened when it did.
The food might have been bad and that caused the internal problem.
If the fish died and produced an ammonia spike then shrimp would have died from that.
If the shrimp died and were not removed for a bit (they were covered in fungus), and you did a water change with alkaline water (pH above 7.0), the ammonia from the dead shrimp could have killed the fish.

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You can just wash the tank out and refill it and let it run for a week before adding anything new.
Or you can add a heap of salt to the tank (so it can no longer dissolve), let it run through the filter for 24 hours, then drain, rinse and set it back up. Wait a week and add fish.

You will have to monitor the water quality because the filters will have to cycle again.

Rinse the live plants with fresh water and put them in a bucket of water and put the tank light above them. Change the water daily until the tank is set back up. Use tap water but do not dechlorinate it and the chlorine will kill off any bugs on the plants without harming the plants. Then put the plants back in the tank.

Did you use a holiday block/auto feeder while you were away?
What were the water conditions when you got home - "not bad for not having been changed" doesn't say how bad they were.