All of the above. We need lots of info, which means you need to get some test kits.
Adding CO2, then withdrawing it is like a cold turkey treatment for your plants. I see no comments about what fertilizers you are using so, if you aren't using any, you will be lacking many key nutrients. A water softener removes magnesium and calcium, which are critical to plants. You should have a bypass on your softener. If it were me, I'd start by engaging that bypass on your filter and then doing 2-3 50% water changes over a day or two (remember to re-engage the water softener after you fill your tank).
You would probably benefit from reading some basic guides, such as here: https://www.plantedtank.net/forums/P...TankGuide.html
, here: https://sites.google.com/site/aquati...ertilizer/home
or here: https://www.advancedplantedtank.com/
Here is another list of info that would help us (which may have duplication of the other posters):
- Light (make & model): ideally, PAR and PUR reading at the substrate and photoperiod?
- CO2 setup (if any) and how you measure CO2 levels in the water if you do inject CO2?
- pH difference between fully de-gassed and fully gassed?
- Current NO3, PO4, GH, KH, pH and TDS readings?
- What you are dosing (product and quantity) and how often?
- Substrate type and how long has it been in place?
- What is your filter setup?
- Cleaning regimen (filter and water change frequency and amount)?
- Circulation: surface rippling and are all plants gently moving from top to bottom?
Here is a list of basic test kits that I like:
PO4: Salifert. Note: above 3ppm, dilute 5:1 with RO or distilled water, then multiply result by 5
GH/KH: API or Sera
Total ammonia: Salifert