DWC Heater, possible noob mistake

Hi guys, ive been having lots of apparently deffiencies and leaf sagging that i really cant get my head around a cause. Then i was thinking, the healthiest plant is furthest away from the water heater and the sickest plant is right on the heater. I originally thought it was important to have the heater there because i thought the plants didnt like the 10 degree dip at night time, but im thinking its doing alot more harm than good. Do you guys think this could be my cause? Do you even use a water heater? It might be a noob mistake i think haha, im still learning!

This is the sort of heater im using by the way =], is it making my plants sad? =[

I doubt that's the problem but you can out the heating element in a glass jar then put it in the water to prevent roots from touching it.

I just took the heater out of the tank and it was just loose on the bottom, floating around, the end of it gets quite hot, there was probably nothing stopping the roots wrapping around the really hot end of the heater. Has anyone ever heard of aquarium heaters causing problems in DWC?

What temperature is your reservoir at without the heater? 58* is a great
temp to be at in your rootzone, so if you can get there naturally enjoy it!

I think the 10* shift at night is for your canopy temperatures, but even 10
isn't that much.

I've never heard of a heater directly causing a plant to not do as well, but
if it's warming up your rootzone in that area to over 75* it could definitely
make things worse.