it has been years before I come back to visit this forum again, the commercially available co2 systems for planted aquarium, are still the same as about 10 years ago...

I am holding on my own DIY co2 systems,

not easy to find the liquidated or used parts now, but this is my personal co2 system that I built back in 2012-2013, only cost me about USD $150, the original price of the parts involved is USD $2500+.