With the range that your room goes through, your res temp is probably just fine.
The only thing I see in your system that is a big unknown is the water. Spring water? Is it for drinking? When you get your ppm meter, stick it in there. Also do you ahve other water options? A lot of water meant for drinking has a lot of sodium in it that you don't want, so in some cases even tap water is safer.
The low dose peroxide treatment recommended above should help clear up the slime, and always make sure you have LOTS of bubbles in the bucket! Root rot loves low oxygen conditions. And if you run a beneficial bacteria in your res to prevent future slime issues, that is good too. But it is one or the other because the peroxide kills bennies too.