Tomatoes and peppers just do better in Dutch buckets (3 to 5 gallons) or Kratky or self-watering containers of a decent size. NFT works best for lettuce and herbs. I use 5 gallon Dutch buckets with the the main lines covered, and the reservoir (110 gallons) buried, and the water still gets up to around 80 F in summer. A temperature goes up, O2 in the solution goes down. But plants can also absorb O2 from the air IF their roots are not completely submerged. My plants look fine even with daytime temps of 104 F.
Also, the roots of tomatoes and peppers can obstruct the flow through the PVC in NFT as the plants get bigger. I remembered this guy's video from several years back. I think he ultimately gave up on NFT toms and peppers.