Hello. I have a 75 gallon Cichlid tank that I've had for years. I have two canister filters and an undergravel filter; I keep the water around 80 degrees and the pH at about 7.8 or so; I use Seachem Malawi Lake Salt and StressCoat during water changes (which I don't do as often as I should, so Nitrates are usually high). I was stupid a few days ago and over-cleaned it; I changed probably 70% of the water, cleaned both filters, and added new Charcoal, StressCoat and Bacterial Supplement. The water was initially very clear, but then became cloudy (looks like smoke in the water). The fish were OK at that time, but I added AmmoLock and aerated the water as a precaution, expecting an Ammonia spike. The next day, I added more AmmoLock and bacteria and within an hour, nearly ALL of my fish were dead! I only was able to save my large Pleco, a couple Autocats and some Convicts. I lost about $400-$500 bucks worth of very nice, large Cichlids.

So, after recovering from that... I did another complete water change to try to get the Ammonia back down, added the supplements, and put the remaining fish back in the tank. Today, it's cloudy again and I'm not sure the best thing to do to avoid losing the other fish, or to prevent me from having this happen in the future.

Is this a cycle problem? Will it resolve itself, and if so, how long? What can I do to keep the fish safe until it does? How can I avoid this in the future?

Any input would be helpful!
Thanks!

You panicked and literally loved your fish to death. Don't be so hard on yourself. You will learn by mistakes
Along the way. Its normal.
Did you ever check the ammonia level? If your ammonia was very high, it was necessary to change large volumes of water to bring it down to save your fish, and only then. Once you add ammo lock ammonia is rendered harmless to your fish, but test kits will still show high levels, ignore it. As the name implies the ammonia is locked up.

The cloudy water is normal when you change that much volume, it must cycle. It clears up in about a week, be patient next time.

P.S. I'm doing this 50 years and still don't know it all. I still make mistakes(: