The weirdest thing happened today

[simon]

. I looked all my plants this morning and everything looked fine especially my one tomato plant that's been doing excellent. 2 hours later I walk out and my tomato plant looks like somebody killed it. It was all droopy and it looked like somebody sucked the life out of it. I changed the water added new nutrient and it looks like it may be coming back to life. Can someone tell me what can cause something like that to happen so suddenly .Please anyone have any ideas so I can avoid this for the future .

FYI: My tomato plant is growing in a 5 gallon bucket, the PH in the water is 6.5, the roots are a beautiful white ,and the sandstone is working fine. I thought I would give you the growing conditions for that particular plant.
Thank you
Simon