Do you have leafy greens in other containers or only the floating raft?

yes, as i said. Some salads and stem cabbage (even younger) on the IBC container (higher level than dwc table) right over the table. Those are in substrate, not hydro.

You should measure the air temperarure in the dwc between the water and the lid :)

Wilting during the day when there is heat and recovering at night is usually an indication of roots issues or some form of bacterial or fungal wilt. Both of those will create problems with the plants being able to transpire properly meaning they can't take up water efficiently so when it's hot they will wilt. When it cools off at night, they recover.

They definitely have access to enough water since it's a raft so how do the roots look?

Water temp of 20C is fine. When you say it got hot, how hot and what was the temp prior? Reason I am asking is that there is a possibility that if it got hot enough quickly it could have just been that the plants just weren't equipped, root-wise, to handle a big change that quickly. The increase in heat caused them to transpire more and if the root structures are not robust enough they couldn't take up enough water hence the wilting. That issue is separate from the roots issues I mentioned first which would be root rot.

Thank you

roots are fine from my point if view, chceck

If there is a root rot starting? How to stop it, please?

you are right

i was checking the root one week ago and these are stem cabbage, these do look nice, but i check the whole raft and found the brown roots from the lettuces, two different species :( Pak choi had pleasable root.

So changes the water, cleaned the table with peroxide, removed bad roots (new roots are there, too). Filled the water with ph down some peroxide and Kristalon .. we'll see.

Thank you