So you think the dinner plate and block worked to pull heat away? I take it there was only one plant that was set up like this, right?
Your C temp of 30 is over 90 F. If you take a C temp and double it, then add 32 you get a good idea as to what a temp is in F.
If you having good grows with hydro and can get water temp down, don't leave it for soil. Hydro produces better when done properly. One thing however, is your airflow. I doesn't look like your exhausting enough air to get the heat out. I don't know what your outdoor temp is but for indoor grows, air flow is a very important factor but often overlooked.