look after your plants - dying plants are not going to contribute to a healthy environment
Put the CO2 back
If you’re concerned about current fertilizers, go pick up some Tropica Specialized & Premium (I recommend both when water is very soft - check your comprehensive water report - if it’s anything like mine, tap water is essentially rain water)
If you have low plant mass, or mostly slow growing plants, add more Premium and less Specialized (N & P, plus additional K I believe)
Depending on plant species, you may need to increase KH and/or GH in very soft tap water
I rarely do either, just choose plants that grow well in very soft water - if you can access an old Tropica catalogue, they included hardness & temperature ranges for their plants
In my shrimp tanks, I add some Seachem Equilibrium for Ca, Mg etc (list available on Seachem website)
Honestly I stopped reading your other topic
It’s just too (I’m editing the word I was about to use so as not to offend) ... perhaps more constructive description ...
“many things are possible, few are probable”
In essence you are off chasing unicorns
Sorry perhaps that is still too blunt
Stressed, ill fish - may react adversely to water change (despite there being absolutely nothing wrong with the water, in or out of tank, despite the water being as exact a match as possible etc)
This likely happens as they lack sufficient biochemical reserves (there is no excess biochemically stored energy - usual state for every cell is to have some excess energy store) so when they are just barely maintaining a semblance of normal appearance/behaviour
anything that alters their environment, leaves them stumbling about (loss of balance, inability to maintain position in water, gasping etc etc)
Rather than trying to deal with the myriad
possible aspects of a planted aquarium,
- just transfer all fish to a sterile bin (any food safe plastic will do if you can’t find an economic glass box- which really just makes observations easier for us),
- maintain temperature,
- dim lighting,
- air driven sponge filter will provide aeration/gentle flow without current (lower energy output for struggling fish),
it won’t be cycled so daily water changes plus a product such as Seachem Stabilty (at recommended dosage) or Prime (at 5-10X dose to manage ammonia, nitrites, this “lasts” ~24h under general conditions, so dose daily regardless of water change)
You could transfer media from existing filter, but only move ceramic type media (no sponge or floss as that may have pathogen contamination)
It is important to choose a bin/aquarium that meets the space (high fish density is a stressor, especially mixed species) and swim/movement requirements of the various species (Rummy Nose need more swim length than Neons) - again this is about minimizing fish stress (which is a much more real thing than the maybe aspect of too soft water somehow killing your fish, or the maybe leaching of toxins from whatever)
You also want a low fish density to minimize possible pathogen transfer between individual fish
Without any idea which medication to use, none is best
If you see signs of Ich, then use a suitable remedy
If tiny air bubbles are “sticking” to fish (re comment above), then you
might add a product such as Seachem Stress Guard (as this may indicate poor/limited slime coat production ... again not an unusual symptom in sick fish)
https://www.seachem.com/stressguard.php
It’s important to read all the FAQ (eg don’t use with any copper based meds)
Seachem is always my recommended brand as they provide more transparency than any other company