Is my pot too small?

as others said, pot size isnt to small...could be deficiency or over watering

I grow in 6L pot and my plants reach up to 1m20, so no 10L isn't too small

Your pot size is just fine... You've got a deficiency of some kind (nitrogen? calcium?) going on and that is usually the result of the PH in the soil not being in a good range so the plant can't absorb the nutes you're giving it. This has most likely resulted in a lockout but that's easily fixed... You'll need to flush (30L of PH balanced water per pot) until the runoff is in a good range - growing in soil, you'll want the PH to be between 6.0 and 6.5. Then give it another gallon of PH'd water with your nutes ... let it dry completely before watering/feeding again. Don't expect the damaged leaves to recover because they won't - but you shouldn't see further problems in other leaves... Make sure your PH is in that range no matter whether you're feeding or watering... If you don't have one, get a good PH pen (I like Apera myself) ... the cost of it will MORE than be compensated for by avoiding future problems like this! Good luck!

The problem here isn't the size of the pot. You might have a nutrient lockout. I recommend watering with pH 6.2 water and TDS 260ppm and measuring the same values in the runoff water. Then post the results in another question to help you out.! xD Good vibes!👌

I can't say what it is but it isn't the pot. You can even grow plants in 1l pots if you'd like. As long as you provide food for their needs it will do. So by saying that the solution would probably to feed them. If you really want to only give water and put them in a pot you gonna need a big pot. Better just re use the soil and feed it yourself organically imo. Hope this helps.

No not really. I'm using 9L and they seem to do fine.