Fizzy water is CO2, not oxygen. U can foilar feed with epsom salts but I dont think that is your prob. Everyone thinks it is a magic cure but it adds loads of salt to your medium and can cause u problems down the road.
Is there a reason u are hesitant to start nutes? U are probably missing out on 50% growth by not using nutes. My friend grew in miracle grow soil w/o using any extra nutes, but the soil had three months worth supposedly. He got 6 ounces off of 12 plants under 1000watts. Next go he used nutes per my suggestion and did everything else exactly the same and he got 1.25 lbs, over 3 times as he did without. I agree with Jester, u should be using nutes. I would go atleast 800ppm if u have a developed rootzone. I havent grown from seed in a while but with my clones, I feed them 1400ppm right out of the rooting chamber when they look like this.
View attachment 353408
View attachment 353409
If they dont have a solid root zone, like these dont
View attachment 353080
they dont survive.