Hi, I am so sorry to hear your cycle crashed. It kinda ruins everything. Also sorry to hear about the loss of your 3rd fish.
How is the fish?
This article will have good suggestions about getting to the cycled point again.
Another member recently used a bottle of Clarity and helped her cycle quickly. Not usually into this sort of stuff but you need any help possible it sounds like!
https://www.aquariumadvice.com/i-just-learned-about-cycling-but-i-already-have-fish-what-now/
Not sure how the cycle crashed but just go you know, you can always use treated / Prime tap water to rinse out the bioballs, other media.
Also for future cleaning, try doing a part at a time.
Substrate on a large tank, half the substrate one week, half the next week. You can still do pwc as needed.
in a couple weeks do a rinse of the filter media, or even half at a time if there is a very large amount. You can even do several rinses of parts over 3 weeks.
Then another week, scrape glass or other things in the tank.
Cleaning in this rotating way can preserve as much BB as possible and help the tank maintain stability.
If it was a super long time since cleaning the bioballs (for the future) - you can also just rinse gently to get rid of the big gunk, then another time focus more on the the crud in the crevices of the ball.
Point being not destroying the mass of BB you have colonized in the tank.
Additionally, if it has been a long time since water changes, do 2, lets say 20-25% pwc one right after the other. Then after half a day, do another larger pwc, like 30%.
The old water in the tank is very different than the new water (like a whole tank clean out) very large water change.
So what you are doing is creating a gentle transition from one water type / old water to the newer fresh water. Doing it gradually will reduce shock.
