Indoor companions in the same container? I already use the CO2 mushroom bags. But what about in with the plants container an in an indoor grow?

Mixing companion plants indoors is a bit of an interesting one - nutrient fixing plants are slow to 'fix' nutrients such as Nitrogen., I'd suggest it for outdoors where you arent going to uproot a plant and over turn all the soil and damage the fungus network so much as you would with a 10L pot, companion plants are better for long term relationships. Using a fungus and adding bacteria beneficial to the rhizosphere is your best way if fixing nutrients, if you add companion plants you can see good results but primarily in no till set ups. I use the techniques with companion plants for my veg garden and my tomato plants are about 4 - 5 feet tall, but using them indoor may just prove hassle. You can water beneficial bacteria in as a top dressing so if you're already part way through a g you can still get the benefits and boost your microbial activity massively, the microbes breaking down the organic matter and sending it on to the fungus which essentially expand the rootzone by adding viable nutrient exchange surface area, in turn your plants exchange nutrients and sugars with the fungus and everuthing grows harmoniously. I've decided to use fungus and bacteria in my 2nd indoors grow and I can see the difference already, I wouldn't bother with companion planting. The CO2 from a small amount of companion planting indoors would be negligible, you're better off using the CO2 bags and maybe watering with some low TDS fizzy water, those bubbles are pure CO2.