Hi my plants suffered from overwatering when they had like 2-3 weeks old

Overwatering is never caused by normal irrigation. 1) fully saturate - minimal runoff so you don't waste those amendments you paid for in your living soil 2) wait for appropriate dryback and repeat - e.g. letting the top 1" dry is a good trigger for a high water capacity medium. If this basic procedure causes droop or problems, it is the fault of your medium. Add more drainage/aeration amendments like perlite or vermiculite. For a high water capacity medium, you want 50% perlite/vermiculite or similar... in something made of coco coir you need 33%. In the end, both contexts end up holding roughly the same volume of water per pot - no accident. if the droopiness is occuring only after an irrigation, ti's the fault of the medium. Not much you can do about it midstream. Next time constitute it with better drainage/aeration properties as explained. more than one thing can cause skinny new growth, too much light, too much K, too much P. New node growth spacing is the simplest way to assess light intensity. How much light depends on various local variables, so it won't always be the same for every garden... node spacing is how you fine-tune it. Too tight and it needs less... too stretched and it needs more. simple. I don't see signs of P or K toxicity, so i'd lean toward too much light being the problem. Too much light, if only slightly too much, can take a week or more to show symptoms. It may tolerate it intiailly but eventually wear down from the stress and not show signs of droop for quite some time. Growht may even seem fine initially but eventualyl that stalls out too. If that sounds familiar, raise the light. No info on light but you can take the specs and do some common sesne extrapolations... For 18 hour vege/auto operation, you only need ~500-600 PPFD. For 12 hours, you need 150% more to equal the same light provided per day over fewer hours - 800-900 PPFD. Take your umol/s PAR production of the light and divide by area in meters-squared. This gives the max PPFD the light could produce. IT'll always be less than this in practice, fwiw. With typical hanging distnaces and reflective walls, you can expect 35-40 DLI to be up near the top of what you can give with ambient CO2. Your climate will impact how much a plant can handle each day, too. so, a 300mol/s light coveringn .5m^2 would be ~600 ppfd. If you then reference a DLI table with hours of operation (18) you'll see it equates to 38.9 DLI. Now, that's a good starting point, and it will speed up the trial and error to dial it in correctly using the plant in front of you as a guide. Like i said, with so many variables, your "max" is not likely the same as someone else's. Use the growth pattern to dial ina healthy amount of light... too lanky, needs more; too tight, needs less... simple. The math just gets you within 5-15% of power... dimmer can dial in the rest. Figure the percent power is proportional to umol/s PAR output. It won't be more than 1-2% off in that regard. So 50% would be 150umol/s PAR etc... Hanging distance should be about teh geometry of even light coverage from end to end without sacrificingn overall average... Hanging distance shouldn't change, but some less-than-ideal contexts may require it.

Still looks like too much water to me. I guess there’s not enough oxygen in the root zone.

Puffy leaves can come from many factors, mostly overwatering, or too intense light. Your plants are just the best measurement tool to know there’s a problem under the soil with the roots. Back up your light first, and boost the roots with some roots enhancers. Recovering takes about 2 weeks for a plant.