First and foremost.....FILL THAT DARN NETPOT! You can't have light making it's way into your bucket. Also that net pot it freaking huge! That poor little plants roots had to fight and shove through a mile of hydroton before it got to open water. Now I know my experience is limited to only 6 hydro grows but I only use HTG Supply Rhizocore net pot/bucket tops. My tap root is in the bucket by day 2. Also while there are some people that make it work as a newbie and not knowing what your tap water is either go pick up a cheap 50GPD RO/Di filter($70) or use RO water from the store. Don't risk a grow with unknown water problem. Start with a clean slate and it will be one thing to rule out. At this point you just need enough to fill your bucket and maybe an extra gallon to top up any evaporation. Once things get rolling and she starts burning through a gallon or two of water a day a RO/DI filter will pay for itself in 1 grow.
As for bucket temps I know I have said it before but my buckets run into the low 80's at the start of my grows. Right now my bucket is 74 degrees. I use Hydroquard.
Here is the underside of a Rhizocore net pot/bucket top and the tap root of my current FastBuds BlackBerry. In this picture the plant was 3 days from sprout. The tap root grows straight down and the feed roots will branch off from it and work their way through the hydroton....
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So to sum it up.....
* Replace and refill your bucket with RO water from the store.
*FILL THE NET POT ALL THE WAY!
* Don't worry so much about bucket temps right now unless they much into the 80's.