Jaden, I've been there as have many of us. It's not easy and very frustrating- especially when you can't pinpoint the problem.
I'm going to suggest a radical solution that I've used myself with good results. You don't have cards, you have cherries and Malawa, so you should be fine. In fact, I've been using this method recently on all my tanks for a "fresh" year. Consider this a water "reset."
Drain your tank of all but 1" or so of water.
Have a bucket of all NEW remin RO water room temp and higher than your tank. Use airline hose to siphon it into your tank.
Simple, but scary right? It works almost 100% of the time when I have old tank syndrome, and even when I want to start the new year fresh like I'm doing now. The side effect is larger and happier shrimp.
By using airline hose instead of dumping it all in at one time, they have a longer time to adjust to it. In addition, it won't stir up all kinds of baddies if using the hose. You don't have to drip, just let it flow. Rest the lid on the hose and walk away. You may get a death or two, (I had maybe 2 out of 32 tanks thus far) but your unknown deaths should slow and stop.
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Of course this method isn't for everyone, just what has worked for me. I only do this extreme of a water change about once/twice a year, unless I have some unknown problem with a tank.